Biography.

Youth and early career.

Petrarch was born in the Tuscan city of Arezzo on 20 July 1304. He was the son of Ser Petracco and his wife Eletta Canigiani. His given name was "Francesco Petracco," which was Latinized to "Petrarca." Petrarch's younger brother was born in Incisa in Val d'Arno in 1307. Dante Alighieri was a friend of his father.  Petrarch spent his early childhood in the village of Incisa, near Florence. He spent much of his early life at Avignon and nearby Carpentras, where his family moved to follow Pope Clement V, who moved there in 1309 to begin the Avignon Papacy. Petrarch studied law at the University of Montpellier (1316–20) and Bologna (1320–23) with a lifelong friend and schoolmate called Guido Sette. Because his father was in the legal profession (a notary), he insisted that Petrarch and his brother also study law. Petrarch, however, was primarily interested in writing and Latin literature and considered these seven years wasted. Additionally, he proclaimed that through legal manipulation his guardians robbed him of his small property inheritance in Florence, which only reinforced his dislike for the legal system. He protested, "I couldn't face making a merchandise of my mind," as he viewed the legal system as the art of selling justice.  Petrarch was a prolific letter writer and counted Boccaccio among his notable friends to whom he wrote often. After the death of their parents, Petrarch and his brother Gherardo went back to Avignon in 1326, where he worked in numerous clerical offices. This work gave him much time to devote to his writing. With his first large-scale work, "Africa", an epic in Latin about the great Roman general Scipio Africanus, Petrarch emerged as a European celebrity. On April 8, 1341, he became the second poet laureate since antiquity and was crowned by Roman "Senatori" Giordano Orsini and Orso dell'Anguillara on the holy grounds of Rome's Capitol.  He traveled widely in Europe, served as an ambassador, and (because he traveled for pleasure, as with his ascent of Mont Ventoux), has been called "the first tourist". During his travels, he collected crumbling Latin manuscripts and was a prime mover in the recovery of knowledge from writers of Rome and Greece. He encouraged and advised Leontius Pilatus's translation of Homer from a manuscript purchased by Boccaccio, although he was severely critical of the result. Petrarch had acquired a copy, which he did not entrust to Leontius, but he knew no Greek; Petrarch said, "Homer was dumb to him, while he was deaf to Homer". In 1345 he personally discovered a collection of Cicero's letters not previously known to have existed, the collection "Epistulae ad Atticum", in the Chapter Library ("Biblioteca Capitolare") of Verona Cathedral.  Disdaining what he believed to be the ignorance of the centuries preceding the era in which he lived, Petrarch is credited or charged with creating the concept of a historical "Dark Ages".

Mount Ventoux.

Petrarch recounts that on April 26, 1336, with his brother and two servants, he climbed to the top of Mont Ventoux (, a feat which he undertook for recreation rather than necessity. The exploit is described in a celebrated letter addressed to his friend and confessor, the monk Dionigi di Borgo San Sepolcro, composed some time after the fact. In it, Petrarch claimed to have been inspired by Philip V of Macedon's ascent of Mount Haemo and that an aged peasant had told him that nobody had ascended Ventoux before or after himself, 50 years before, and warned him against attempting to do so. The nineteenth-century Swiss historian Jacob Burckhardt noted that Jean Buridan had climbed the same mountain a few years before, and ascents accomplished during the Middle Ages have been recorded, including that of Anno II, Archbishop of Cologne.  Scholars note that Petrarch's letter to Dionigi displays a strikingly "modern" attitude of aesthetic gratification in the grandeur of the scenery and is still often cited in books and journals devoted to the sport of mountaineering. In Petrarch, this attitude is coupled with an aspiration for a virtuous Christian life, and on reaching the summit, he took from his pocket a volume by his beloved mentor, Saint Augustine, that he always carried with him. For pleasure alone he climbed Mont Ventoux, which rises to more than six thousand feet, beyond Vaucluse. It was no great feat, of course; but he was the first recorded Alpinist of modern times, the first to climb a mountain merely for the delight of looking from its top. (Or almost the first; for in a high pasture he met an old shepherd, who said that fifty years before he had attained the summit, and had got nothing from it save toil and repentance and torn clothing.) Petrarch was dazed and stirred by the view of the Alps, the mountains around Lyons, the Rhone, the Bay of Marseilles. He took Augustine's "Confessions" from his pocket and reflected that his climb was merely an allegory of aspiration toward a better life. As the book fell open, Petrarch's eyes were immediately drawn to the following words: Petrarch's response was to turn from the outer world of nature to the inner world of "soul":  James Hillman argues that this rediscovery of the inner world is the real significance of the Ventoux event. The Renaissance begins not with the ascent of Mont Ventoux but with the subsequent descent—the "return [...] to the valley of soul", as Hillman puts it. Arguing against such a singular and hyperbolic periodization, Paul James suggests a different reading:

Later years.

Petrarch spent the later part of his life journeying through northern Italy as an international scholar and poet-diplomat. His career in the Church did not allow him to marry, but he is believed to have fathered two children by a woman or women unknown to posterity. A son, Giovanni, was born in 1337, and a daughter, Francesca, was born in 1343. He later legitimized both. Giovanni died of the plague in 1361. In the same year Petrarch was named canon in Monselice near Padua. Francesca married Francescuolo da Brossano (who was later named executor of Petrarch's will) that same year. In 1362, shortly after the birth of a daughter, Eletta (the same name as Petrarch's mother), they joined Petrarch in Venice to flee the plague then ravaging parts of Europe. A second grandchild, Francesco, was born in 1366, but died before his second birthday. Francesca and her family lived with Petrarch in Venice for five years from 1362 to 1367 at Palazzo Molina; although Petrarch continued to travel in those years. Between 1361 and 1369 the younger Boccaccio paid the older Petrarch two visits. The first was in Venice, the second was in Padua.  About 1368 Petrarch and his daughter Francesca (with her family) moved to the small town of Arquà in the Euganean Hills near Padua, where he passed his remaining years in religious contemplation. He died in his house in Arquà early on July 20, 1374—his seventieth birthday. The house hosts now a permanent exhibition of Petrarchian works and curiosities; among others you find the famous tomb of Petrarch's beloved cat who was embalmed. On the marble slab there is a Latin inscription written by Antonio Quarenghi: Petrarch's will (dated April 4, 1370) leaves 50 florins to Boccaccio "to buy a warm winter dressing gown"; various legacies (a horse, a silver cup, a lute, a Madonna) to his brother and his friends; his house in Vaucluse to its caretaker; for his soul, and for the poor; and the bulk of his estate to his son-in-law, Francescuolo da Brossano, who is to give half of it to "the person to whom, as he knows, I wish it to go"; presumably his daughter, Francesca, Brossano's wife. The will mentions neither the property in Arquà nor his library; Petrarch's library of notable manuscripts was already promised to Venice, in exchange for the Palazzo Molina. This arrangement was probably cancelled when he moved to Padua, the enemy of Venice, in 1368. The library was seized by the lords of Padua, and his books and manuscripts are now widely scattered over Europe. Nevertheless, the Biblioteca Marciana traditionally claimed this bequest as its founding, although it was in fact founded by Cardinal Bessarion in 1468.

Works.

Petrarch is best known for his Italian poetry, notably the "Rerum vulgarium fragmenta" ("Fragments of Vernacular Matters"), a collection of 366 lyric poems in various genres also known as 'canzoniere' ('songbook'), and the "Triumphi" ("Triumphs"), a six-part narrative poem of Dantean inspiration. However, Petrarch was an enthusiastic Latin scholar and did most of his writing in this language. His Latin writings include scholarly works, introspective essays, letters, and more poetry. Among them are "Secretum" ("My Secret Book"), an intensely personal, imaginary dialogue with a figure inspired by Augustine of Hippo; "De Viris Illustribus" ("On Famous Men"), a series of moral biographies; "Rerum Memorandarum Libri", an incomplete treatise on the cardinal virtues; "De Otio Religiosorum" ("On Religious Leisure") and "De Vita Solitaria" ("On the Solitary Life"), which praise the contemplative life; "De Remediis Utriusque Fortunae" ("Remedies for Fortune Fair and Foul"), a self-help book which remained popular for hundreds of years; "Itinerarium" ("Petrarch's Guide to the Holy Land"); invectives against opponents such as doctors, scholastics, and the French; the "Carmen Bucolicum", a collection of 12 pastoral poems; and the unfinished epic "Africa". He translated seven psalms, a collection known as the "Penitential Psalms".  Petrarch also published many volumes of his letters, including a few written to his long-dead friends from history such as Cicero and Virgil. Cicero, Virgil, and Seneca were his literary models. Most of his Latin writings are difficult to find today, but several of his works are available in English translations. Several of his Latin works are scheduled to appear in the Harvard University Press series "I Tatti". It is difficult to assign any precise dates to his writings because he tended to revise them throughout his life.  Petrarch collected his letters into two major sets of books called "Rerum familiarum liber" ("Letters on Familiar Matters") and "Seniles" ("Letters of Old Age"), both of which are available in English translation. The plan for his letters was suggested to him by knowledge of Cicero's letters. These were published "without names" to protect the recipients, all of whom had close relationships to Petrarch. The recipients of these letters included Philippe de Cabassoles, bishop of Cavaillon; Ildebrandino Conti, bishop of Padua; Cola di Rienzo, tribune of Rome; Francesco Nelli, priest of the Prior of the Church of the Holy Apostles in Florence; and Niccolò di Capoccia, a cardinal and priest of Saint Vitalis. His "Letter to Posterity" (the last letter in "Seniles") gives an autobiography and a synopsis of his philosophy in life. It was originally written in Latin and was completed in 1371 or 1372—the first such autobiography in a thousand years (since Saint Augustine).  While Petrarch's poetry was set to music frequently after his death, especially by Italian madrigal composers of the Renaissance in the 16th century, only one musical setting composed during Petrarch's lifetime survives. This is "Non al suo amante" by Jacopo da Bologna, written around 1350.

Laura and poetry.

On April 6, 1327, after Petrarch gave up his vocation as a priest, the sight of a woman called "Laura" in the church of Sainte-Claire d'Avignon awoke in him a lasting passion, celebrated in the "Rerum vulgarium fragmenta" ("Fragments of Vernacular Matters"). Laura may have been Laura de Noves, the wife of Count Hugues de Sade (an ancestor of the Marquis de Sade). There is little definite information in Petrarch's work concerning Laura, except that she is lovely to look at, fair-haired, with a modest, dignified bearing. Laura and Petrarch had little or no personal contact. According to his "Secretum", she refused him because she was already married. He channeled his feelings into love poems that were exclamatory rather than persuasive, and wrote prose that showed his contempt for men who pursue women. Upon her death in 1348, the poet found that his grief was as difficult to live with as was his former despair. Later in his "Letter to Posterity", Petrarch wrote: "In my younger days I struggled constantly with an overwhelming but pure love affair—my only one, and I would have struggled with it longer had not premature death, bitter but salutary for me, extinguished the cooling flames. I certainly wish I could say that I have always been entirely free from desires of the flesh, but I would be lying if I did". While it is possible she was an idealized or pseudonymous character—particularly since the name "Laura" has a linguistic connection to the poetic "laurels" Petrarch coveted—Petrarch himself always denied it. His frequent use of "l'aura" is also remarkable: for example, the line "Erano i capei d'oro a "l'aura" sparsi" may both mean "her hair was all over Laura's body", and "the wind ("l'aura") blew through her hair". There is psychological realism in the description of Laura, although Petrarch draws heavily on conventionalised descriptions of love and lovers from troubadour songs and other literature of courtly love. Her presence causes him unspeakable joy, but his unrequited love creates unendurable desires, inner conflicts between the ardent lover and the mystic Christian, making it impossible to reconcile the two. Petrarch's quest for love leads to hopelessness and irreconcilable anguish, as he expresses in the series of paradoxes in Rima 134 "Pace non trovo, et non ò da far guerra;/e temo, et spero; et ardo, et son un ghiaccio": "I find no peace, and yet I make no war:/and fear, and hope: and burn, and I am ice".  Laura is unreachable and evanescent – descriptions of her are evocative yet fragmentary.Francesco De Sanctis on the powerful music of his verse in his "Storia della letteratura italiana". Gianfranco Contini, in a famous essay ("Preliminari sulla lingua del Petrarca". Petrarca, Canzoniere. Turin, Einaudi, 1964) has described Petrarch's language in terms of "unilinguismo" (contrasted with Dantean "plurilinguismo").

Dante.

Petrarch is a world apart from Dante and his "Divina Commedia". In spite of the metaphysical subject, the "Commedia" is deeply rooted in the cultural and social milieu of turn-of-the-century Florence: Dante's rise to power (1300) and exile (1302); his political passions call for a "violent" use of language, where he uses all the registers, from low and trivial to sublime and philosophical. Petrarch confessed to Boccaccio that he had never read the "Commedia", remarks Contini, wondering whether this was true or Petrarch wanted to distance himself from Dante. Dante's language evolves as he grows old, from the courtly love of his early stilnovistic "Rime" and "Vita nuova" to the "Convivio" and "Divina Commedia", where Beatrice is sanctified as the goddess of philosophy—the philosophy announced by the Donna Gentile at the death of Beatrice.  In contrast, Petrarch's thought and style are relatively uniform throughout his life—he spent much of it revising the songs and sonnets of the "Canzoniere" rather than moving to new subjects or poetry. Here, poetry alone provides a consolation for personal grief, much less philosophy or politics (as in Dante), for Petrarch fights within himself (sensuality versus mysticism, profane versus Christian literature), not against anything outside of himself. The strong moral and political convictions which had inspired Dante belong to the Middle Ages and the libertarian spirit of the commune; Petrarch's moral dilemmas, his refusal to take a stand in politics, his reclusive life point to a different direction, or time. The free commune, the place that had made Dante an eminent politician and scholar, was being dismantled: the "signoria" was taking its place. Humanism and its spirit of empirical inquiry, however, were making progress—but the papacy (especially after Avignon) and the empire (Henry VII, the last hope of the white Guelphs, died near Siena in 1313) had lost much of their original prestige.  Petrarch polished and perfected the sonnet form inherited from Giacomo da Lentini and which Dante widely used in his "Vita nuova" to popularise the new courtly love of the "Dolce Stil Novo". The tercet benefits from Dante's terza rima (compare the "Divina Commedia"), the quatrains prefer the ABBA–ABBA to the ABAB–ABAB scheme of the Sicilians. The imperfect rhymes of "u" with closed "o" and "i" with closed "e" (inherited from Guittone's mistaken rendering of Sicilian verse) are excluded, but the rhyme of open and closed "o" is kept. Finally, Petrarch's enjambment creates longer semantic units by connecting one line to the following. The vast majority (317) of Petrarch's 366 poems collected in the "Canzoniere" (dedicated to Laura) were "sonnets", and the Petrarchan sonnet still bears his name.

Philosophy.

Petrarch is traditionally called the father of Humanism and considered by many to be the "father of the Renaissance." In his work "Secretum meum" he points out that secular achievements did not necessarily preclude an authentic relationship with God. Petrarch argued instead that God had given humans their vast intellectual and creative potential to be used to their fullest. He inspired humanist philosophy which led to the intellectual flowering of the Renaissance. He believed in the immense moral and practical value of the study of ancient history and literature—that is, the study of human thought and action. Petrarch was a devout Catholic and did not see a conflict between realizing humanity's potential and having religious faith.  A highly introspective man, he shaped the nascent humanist movement a great deal because many of the internal conflicts and musings expressed in his writings were seized upon by Renaissance humanist philosophers and argued continually for the next 200 years. For example, Petrarch struggled with the proper relation between the active and contemplative life, and tended to emphasize the importance of solitude and study. In a clear disagreement with Dante, in 1346 Petrarch argued in his "De vita solitaria" that Pope Celestine V's refusal of the papacy in 1294 was as a virtuous example of solitary life. Later the politician and thinker Leonardo Bruni (1370–1444) argued for the active life, or "civic humanism". As a result, a number of political, military, and religious leaders during the Renaissance were inculcated with the notion that their pursuit of personal fulfillment should be grounded in classical example and philosophical contemplation.

Legacy.

Petrarch's influence is evident in the works of Serafino Ciminelli from Aquila (1466–1500) and in the works of Marin Držić (1508–1567) from Dubrovnik.  The Romantic composer Franz Liszt set three of Petrarch's Sonnets (47, 104, and 123) to music for voice, "Tre sonetti del Petrarca", which he later would transcribe for solo piano for inclusion in the suite "Années de Pèlerinage". Liszt also set a poem by Victor Hugo, " O quand je dors" in which Petrarch and Laura are invoked as the epitome of erotic love.  While in Avignon in 1991, Modernist composer Elliott Carter completed his solo flute piece "Scrivo in Vento" which is in part inspired by and structured by Petrarch's Sonnet 212, "Beato in sogno". It was premiered on Petrarch's 687th birthday.  In November 2003, it was announced that pathological anatomists would be exhuming Petrarch's body from his casket in Arquà Petrarca, in order to verify 19th-century reports that he had stood 1.83 meters (about six feet), which would have been tall for his period. The team from the University of Padua also hoped to reconstruct his cranium in order to generate a computerized image of his features to coincide with his 700th birthday. The tomb had been opened previously in 1873 by Professor Giovanni Canestrini, also of Padua University. When the tomb was opened, the skull was discovered in fragments and a DNA test revealed that the skull was not Petrarch's, prompting calls for the return of Petrarch's skull.  The researchers are fairly certain that the body in the tomb is Petrarch's due to the fact that the skeleton bears evidence of injuries mentioned by Petrarch in his writings, including a kick from a donkey when he was 42.

Francesco Petrarca (; July 20, 1304 – July 18/19, 1374), commonly anglicized as Petrarch (), was an Italian scholar and poet during the early Italian Renaissance who was one of the earliest humanists.

Francesco Petrarca ([frančesko petrarka]; 20. července 1304 – 18./19. července 1374) byl italský spisovatel a básník. Společně se svým vrstevníkem a přítelem Boccacciem je považován za jednoho z prvních autorů renesanční literatury. Bývá označován za největšího humanistu a nejvlivnějšího italského lyrického básníka. Tvořil v latině i v italštině a jeho nejproslulejším dílem je italsky psaný "Zpěvník", popisující v 366 básních zejména platonickou lásku k idealizované Lauře. Petrarcova latinská tvorba zahrnuje smyšlený dialog básníka se svatým Augustinem známý jako "Mé tajemství", filosofický traktát "O lécích proti štěstí a neštěstí" nebo polemické spisy proti lékařům či aristotelikům. Svým dílem navazoval jak na Vergilia, Ovidia, Cicerona, Senecu, svatého Augustina a další antické autory, tak na pozdně středověkého Danta Alighieriho.


History.

The predecessor of militias were armed groups of factory workers ("Závodní milice", factory militias) formed in June 1945 to protect the factories during the post-war chaos. In 1946 they were renamed "Závodní stráže" ("factory guards") and their equipment reduced to pistols.  In the middle of February 1948 the central committee of the Communist Party decided to form armed units from Communist Party members and supporters. On February 21, 1948 these units were renamed "Dělnické milice" ("Worker's Militias"). The militias were hastily equipped and set on alert during the communist takeover of power at the end of February. The name was soon changed to "People's Militias".

Tasks.

The task of the militias was to protect against guerrillas expected to appear after the takeover, against undercover agents sent to Czechoslovakia and to cooperate with the police and the army. About 3,000 militiamen joined police forces. Non-communists were slowly removed from the militias. The control over the militias went to the Ministry of the Interior.  In 1952 the official status of the militias changed to being the armed part of the Communist Party of Czechoslovakia and control passed to the Communist Party (to the newly established departments at the central committee); also the organisational structure was changed. In 1959 a grey uniform was introduced.  Toward the end of the 1980s, political tensions in Czechoslovakia increased and the militias, equipped with batons, were frequently deployed to disperse demonstrations against the regime. In 1989, 38,985 militiamen participated in this activity.  After the communist party's fall from power at the end of 1989, the militias were dissolved on 21 December 1989.

Numbers and armament.

During February 1948 the militias obtained 10,000 rifles and 2,000 submachine guns from the armament factory Zbrojovka Brno. The equipment was continually modernized with sniper rifles, machine guns, mortars, anti-aircraft machine guns and transport vehicles. The ammunition was kept in army stores. During the 1970s recoilless guns and RPG-7 were added among the armament. After dissolution of the militias their equipment was handed over to the army.

Military equipment at 1989.

20,067 pistols (with over 4 million rounds) 71,054 submachine guns (with over 62 million rounds) 6,890 machine guns (with over 16 million rounds) 130 anti-aircraft machine guns (over one million rounds) 358 mortars 149 recoilless guns 2,177 trucks and motorcycles 2,031 hand grenades

See also.

Similar formations:

People's Militias (in Slovak "Ľudové milície", in Czech "Lidové milice"), also called The Armed Fist of the Working Class (in Slovak "Ozbrojená päsť robotníckej triedy", in Czech "Ozbrojená pěst dělnické třídy") was a militia organisation of the Communist Party of Czechoslovakia between 1948 and 1989.

Lidové milice (LM, nazývané též "„ozbrojená pěst dělnické třídy“", slovensky "Ľudové milície", "ĽM") byly dělnické bojové jednotky, o jejichž vzniku rozhodl Ústřední výbor Komunistické strany Československa dne 21. února 1948 při přípravě komunistického převratu v Československu. Vznik a existence Lidových milicí nebyly nikdy upraveny žádným zákonem.


History.

Early years.

Google began in January 1996 as a research project by Larry Page and Sergey Brin when they were both PhD students at Stanford University in Stanford, California. The project initially involved an unofficial "third founder", Scott Hassan, the original lead programmer who wrote much of the code for the original Google Search engine, but he left before Google was officially founded as a company; Hassan went on to pursue a career in robotics and founded the company Willow Garage in

Growth.

In March 1999, the company moved its offices to Palo Alto, California, which is home to several prominent Silicon Valley technology start-ups. The next year, Google began selling advertisements associated with search keywords against Page and Brin's initial opposition toward an advertising-funded search engine. To maintain an uncluttered page design, advertisements were solely text-based. In June 2000, it was announced that Google would become the default search engine provider for Yahoo!, one of the most popular websites at the time, replacing Inktomi. In 2003,

Initial public offering.

Google's initial public offering (IPO) took place five years later, on August 19, 2004. At that time Larry Page, Sergey Brin, and Eric Schmidt agreed to work together at Google for 20 years, until the year 2024. At IPO, the company offered 19,605,052 shares at a price of $85 per share. Shares were sold in an online auction format using a system built by Morgan Stanley and Credit Suisse, underwriters for the deal. The sale of $1.67 billion gave Google a market capitalization of more than $23 billion. In October 2006, Google announced that it had acquired the video-sharing site YouTube for $1.65 billion in Google stock, and the deal was finalized on November 13, 2006. On April 13, 2007, Google reached an agreement

2012 onward.

The year 2012 was the first time that Google generated $50 billion in annual revenue, generating $38 billion the previous year. In January 2013, then-CEO Larry Page commented, "We ended 2012 with a strong quarter... Revenues were up 36% year-on-year, and 8% quarter-on-quarter. And we hit $50 billion in revenues for the first time last year – not a bad achievement in just a decade and a half."  In June 2013, Google acquired Waze, a $966 million deal. While Waze would remain an independent entity, its social features, such as its crowdsourced location platform, were reportedly valuable integrations between Waze and Google Maps, Google's

Products and services.

Search engine.

Google indexes billions of web pages to allow users to search for the information they desire through the use of keywords and operators. According to comScore market research from November 2009, Google Search is the dominant search engine in the United States market, with a market share of 65.6%. In May 2017,

Advertising.

As per its 2017 Annual report, Google generates most of its revenues from advertising. This includes sales of apps, purchases made in-app, digital content products on google and YouTube, android and licensing and service fees, including fees received for Google Cloud offerings. 46% of this was from clicks (cost per clicks), amounting to US$109,652 million in 2017. This includes three principal methods, namely AdMob, AdSense (such as AdSense for Content, AdSense for Search, etc.) and DoubleClick AdExchange.  For the 2006 fiscal year, the company reported $10.492 billion in total advertising revenues and only $112 million in licensing and other revenues. In 2011, 96% of Google's revenue was derived from its advertising programs. In addition to its own algorithms for understanding search requests, Google uses technology from the company DoubleClick, to project

Consumer services.

Web-based services.

Google offers Gmail for email, Google Calendar for time-management and scheduling, Google Maps for mapping, navigation and satellite imagery, Google Drive for cloud storage of files, Google Docs, Sheets and Slides for

Software.

Google develops the Android mobile operating system, as well as its smartwatch, television, car, and Internet

Hardware.

In January 2010, Google released Nexus One, the first Android phone under its own brand, "Nexus". It spawned a number of phones and tablets under the "Nexus" branding until its eventual discontinuation in 2016, replaced by a new brand called Pixel.  In 2011, the Chromebook was introduced, described as a "new kind of computer" running Chrome OS.  In July 2013, Google introduced the Chromecast dongle, that allows users to stream content from their smartphones to televisions.  In June 2014, Google announced Google Cardboard, a simple cardboard viewer that lets user place their smartphone in a special front compartment to view virtual reality (VR) media.  In October 2018, Google announced the Pixel 3. The phone

Enterprise services.

G Suite is a monthly subscription offering for organizations and businesses to get access to a collection of Google's services, including Gmail, Google Drive and Google Docs, Google Sheets and Google Slides, with additional administrative tools, unique domain names, and 24/7 support.  On September 24, 2012, Google launched Google for Entrepreneurs, a largely not-for-profit business incubator providing startups with co-working spaces known as Campuses, with assistance to startup founders that may include workshops, conferences, and

Internet services.

In February 2010, Google announced the Google Fiber project, with experimental plans to build an ultra-high-speed broadband network for 50,000 to 500,000 customers in one or more American cities. Following Google's corporate restructure to make Alphabet Inc. its parent company, Google Fiber was moved to Alphabet's Access division.  In April 2015, Google announced Project Fi, a mobile virtual network operator, that combines Wi-Fi and cellular networks from different telecommunication providers in an effort to enable seamless

Other products.

In May 2011, Google announced Google Wallet, a mobile application for wireless payments.

Corporate affairs.

Finance.

Google's initial public offering (IPO) took place on August 19, 2004. At IPO, the company offered 19,605,052 shares at a price of $85 per share. The sale of $1.67 billion gave Google a market capitalization of more than $23 billion. The stock performed well after the IPO, with shares hitting $350 for the first time on October 31, 2007, primarily because of strong sales and earnings in the online advertising market. The surge in stock price was fueled mainly by individual investors, as opposed to large institutional investors and mutual funds. GOOG shares split into GOOG class C shares and GOOGL class A shares. The company is listed on the NASDAQ stock exchange under the ticker symbols GOOGL and GOOG, and on the Frankfurt Stock Exchange under the ticker symbol GGQ1. These ticker symbols now refer to Alphabet Inc., Google's holding company,  The corporation's consolidated revenue for the third quarter of 2013 was reported in mid-October 2013 as $14.89 billion, a 12 percent increase

Corporate identity.

The name "Google" originated from a misspelling of "googol", which refers to the number represented by a 1 followed by one-hundred zeros. Page and Brin write in their original paper on PageRank: "We chose our systems name, Google, because it is a common spelling of googol, or 10 and fits well with our goal of building very large-scale search engines." Having found its way increasingly into everyday language, the verb "google" was added to the "Merriam Webster Collegiate Dictionary" and the "Oxford English Dictionary" in 2006, meaning "to use the Google search engine to obtain information on the Internet." Google's mission statement, from the outset, was "to organize the world's information and make it universally accessible and useful", and its unofficial slogan is "Don't be evil". In October 2015, a related motto was adopted in the Alphabet corporate code of conduct by the phrase: "Do the right thing". The original motto was retained in the code of conduct of

Workplace culture.

On "Fortune" magazine's list of the best companies to work for, Google ranked first in 2007, 2008 and 2012, and fourth in 2009 and 2010. Google was also nominated in 2010 to be the world's most attractive employer to graduating students in the Universum Communications talent attraction index. Google's corporate philosophy includes principles such as "you can make money without doing evil," "you can be serious without a suit," and "work should be challenging and the challenge should be fun."  Google's employees are hired based on a hierarchical system. Employees are split into six hierarchies based on experience and can range "from entry-level data center workers at level one to managers and experienced engineers at level six." As a motivation technique, Google

Office locations.

Google's headquarters in Mountain View, California is referred to as "the Googleplex", a play on words on the number googolplex and the headquarters itself being a "complex" of buildings. Internationally, Google has over 78 offices in more than 50 countries.  In 2006, Google moved into about of office space in New York City, at 111 Eighth Avenue in Manhattan. The office was designed and built specially for Google, and houses its largest advertising sales team, which has been instrumental in securing large partnerships. In 2010, Google bought the building housing the headquarter, in a deal that valued the property at around $1.9 billion. In March 2018, Google's parent company Alphabet bought the nearby Chelsea Market building for $2.4 billion. The sale is touted as one of the most expensive real estate transactions for a single building in the history of New York. In November 2018, Google announced its plan to expand its New York City

Infrastructure.

Google data centers are located in North and South America, Asia, and Europe. There is no official data on the number of servers in Google data centers; however, research and advisory firm Gartner estimated in a July 2016 report that Google at the time had 2.5 million servers. Traditionally, Google relied on parallel computing on

Environment.

In October 2006, the company announced plans to install thousands of solar panels to provide up to 1.6 megawatts of electricity, enough to satisfy approximately 30% of the campus' energy needs. The system will be the largest solar power system constructed on a U.S. corporate campus and one of the largest on any corporate site in the world. Google has aimed for carbon neutrality in regard to its operations.  Google disclosed in September 2011 that it "continuously uses enough electricity to power 200,000 homes", almost 260

Philanthropy.

In 2004, Google formed the not-for-profit philanthropic Google.org, with a start-up fund of $1 billion. The mission of the organization is to create awareness about climate change, global public health, and global poverty. One of its first projects was to develop a viable plug-in hybrid electric vehicle that can attain 100 miles per gallon. Google hired Larry Brilliant as the program's executive director in 2004 and Megan Smith has replaced him as director.  In 2008, Google announced its "project 10" which accepted ideas for how

Criticism and controversy.

Google's market dominance has led to prominent media coverage, including criticism of the company over issues such as aggressive tax avoidance, search neutrality, copyright, censorship of search results and content, and privacy. Other criticisms include alleged misuse and manipulation of search results, its use of others' intellectual property, concerns that its compilation of data may violate people's privacy, and the energy consumption of its servers, as well as concerns over traditional business issues such as monopoly, restraint of trade, anti-competitive practices, and patent infringement.  Google formerly adhered to the Internet censorship policies of China, enforced by means of filters colloquially known as "The Great Firewall of China", but no longer does so. As a result, all Google services except for Chinese Google Maps are blocked from access within mainland China without the aid of VPNs, proxy servers, or other similar technologies. "The Intercept" reported in August 2018 that Google is developing for the People's Republic of China a censored version of its search engine (known as Dragonfly) "that will blacklist websites and search terms about human rights, democracy, religion, and peaceful protest". However, the project had been withheld due to privacy concerns.  Following media reports about PRISM, NSA's massive electronic surveillance program, in June 2013, several technology companies were identified as participants, including Google. According to leaks of said program, Google joined the PRISM program in 2009.  Google has worked with the United States Department of Defense on drone software through the 2017 "Project Maven" that could be used to improve the accuracy of drone strikes. Thousands of Google employees, including senior engineers, have signed a letter urging Google CEO Sundar Pichai to end a controversial contract with the Pentagon. In response to the backlash, Google ultimately decided to not renew their DoD contract, set to expire in 2019.  Shona Ghosh, a journalist for Business Insider, noted that an increasing digital resistance movement against Google has grown. A major hub for critics of Google in order to organize to abstain from using Google products is the Reddit page for the subreddit /r/degoogle.  In July 2018, Mozilla Program Manager Chris Peterson accused Google of intentionally slowing down YouTube performance on Firefox.  In April 2019 former Mozilla executive Jonathan Nightingale accused Google of intentionally and systematically sabotaging the Firefox browser over the past decade in order to boost Chrome's adoption.  In November 2019, the Office for Civil Rights of the Department of Health and Human Services began investigation into Project Nightingale, to assess whether the "mass collection of individuals’ medical records" complied with HIPAA. According to "The Wall Street Journal", Google commenced the project in secret, in 2018, with St. Louis-based healthcare company Ascension.

Litigation.

Google has been involved in a number of lawsuits including the High-Tech Employee Antitrust Litigation which resulted in Google being one of four companies to pay a $415 million settlement to employees.  On June 27, 2017, the company received a record fine of from the European Union for "promoting its own shopping comparison service at the top of search results." Commenting on the penalty, "New Scientist" magazine said: "The hefty sum – the largest ever doled out by the EU's competition regulators – will sting in the short term, but Google can handle it. Alphabet, Google’s parent company, made a profit of $2.5 billion (€2.2 billion) in the first six weeks of 2017 alone. The real impact of the ruling is that Google must stop using its dominance as a search engine to give itself the edge in another market: online price comparisons." The company disputed the ruling. The hearing at the General Court of Luxembourg was scheduled for 2020. The court is going to deliver the ultimate judgment by the end of the year.  On July

DeGoogle movement.

The term "DeGoogle" has grown in use as privacy activists urge users to sto

Google LLC is an American multinational technology company that specializes in Internet-related services and products, which include online advertising technologies, a search engine, cloud computing, software, and hardware. It is considered one of the Big Four technology companies alongside Amazon, Apple, and Microsoft.

Google ["gu:gl"] je americká společnost sídlící v Mountain View v Silicon Valley jižně od San Francisca v Kalifornii; její areál je přezdíván "Googleplex". Je vlastněna holdingovou společností Alphabet Inc. Od podzimu 2006 je Google oficiálně zastoupen pobočkou v Česku, sídlící v Praze. Společnost je známá především díky svému internetovému vyhledávači, jehož popularita je taková, že se dnes již používá i sloveso "googlovat" či "googlit" ve smyslu "hledat na internetu". V roce 2006 se toto sloveso objevilo v Oxford English Dictionary. Z hlediska českého jazyka se Google skloňuje dle vzoru "hrad" (Google, bez Googlu...).


History.

In December 1994, Theo de Raadt was forced to resign from the NetBSD core team, and his access to the source repository was revoked. Fellow team members claimed it was due to personality clashes on the mailing lists.  In October 1995, De Raadt founded OpenBSD, a new project forked from NetBSD 1.0. The initial release, OpenBSD 1.2, was made in July 1996, followed by OpenBSD 2.0 in October of the same year. Since then, the project has issued a release every six months, each of which is supported for one year.  On 25 July 2007, OpenBSD developer Bob Beck announced the formation of the OpenBSD Foundation, a Canadian non-profit organization formed to "act as a single point of contact for persons and organizations requiring a legal entity to deal with when they wish to support OpenBSD."  It is hard to determine how widely OpenBSD is used, because the developers do not publish or collect usage statistics. In September 2005, the BSD Certification Group surveyed BSD users, showing that 33 percent used OpenBSD, behind FreeBSD with 77 percent and ahead of NetBSD with 16 percent.

Uses.

Network appliances.

OpenBSD features a robust TCP/IP networking stack, and can be used as a router or wireless access point. OpenBSD's security enhancements, built-in cryptography, and packet filter make it suitable for security purposes such as firewalls, intrusion-detection systems, and VPN gateways.  Several proprietary systems are based on OpenBSD, including devices from Armorlogic (Profense web application firewall), Calyptix Security, GeNUA, RTMX, and.vantronix.

Personal computers.

OpenBSD ships with Xenocara, an implementation of the X Window System, and is suitable as a desktop operating system for personal computers, including laptops., OpenBSD includes approximately 8000 packages in its software repository, including desktop environments such as GNOME, Plasma 4, and Xfce, and web browsers such as Firefox and Chromium. The project also includes three window managers in the main distribution: cwm, FVWM (part of the default configuration for Xenocara), and twm.

Servers.

OpenBSD features a full server suite and can be configured as a mail server, web server, FTP server, DNS server, router, firewall, NFS file server, or any combination of these.

Security.

Shortly after OpenBSD was created, De Raadt was contacted by a local security software company named Secure Networks (later acquired by McAfee). They were developing a network security auditing tool called Ballista, which was intended to find and exploit software security flaws. This coincided with De Raadt's interest in security, so the two cooperated leading up to the release of OpenBSD 2.3. This collaboration helped to define security as the focus of the OpenBSD project.  OpenBSD includes numerous features designed to improve security, such as:  To reduce the risk of a vulnerability or misconfiguration allowing privilege escalation, many programs have been written or adapted to make use of privilege separation, privilege revocation and chrooting. Privilege separation is a technique, pioneered on OpenBSD and inspired by the principle of least privilege, where a program is split into two or more parts, one of which performs privileged operations and the other—almost always the bulk of the code—runs without privilege. Privilege revocation is similar and involves a program performing any necessary operations with the privileges it starts with then dropping them. Chrooting involves restricting an application to one section of the file system, prohibiting it from accessing areas that contain private or system files. Developers have applied these enhancements to OpenBSD versions of many common applications, such as tcpdump, file, tmux, smtpd, and syslogd.  OpenBSD developers were instrumental in the creation and development of OpenSSH, which is developed in the OpenBSD CVS repositories. OpenSSH is based on the original SSH. It first appeared in OpenBSD 2.6 and is now by far the most popular SSH client and server, available on many operating systems.  The project has a policy of continually auditing source code for problems, work that developer Marc Espie has described as "never finished... more a question of process than of a specific bug being hunted." He went on to list several typical steps once a bug is found, including examining the entire source tree for the same and similar issues, "try[ing] to find out whether the documentation ought to be amended", and investigating whether "it's possible to augment the compiler to warn against this specific problem."

Security record.

The OpenBSD website features a prominent reference to the system's security record. Until June 2002, it read:  In June 2002, Mark Dowd of Internet Security Systems disclosed a bug in the OpenSSH code implementing challenge-response authentication. This vulnerability in the OpenBSD default installation allowed an attacker remote access to the root account, which was extremely serious not only to OpenBSD, but also to the large number of other operating systems that were using OpenSSH by that time. This problem necessitated the adjustment of the slogan on the OpenBSD website to:  The quote remained unchanged as time passed, until on March 13, 2007, when Alfredo Ortega of Core Security Technologies disclosed a network-related remote vulnerability. The quote was subsequently changed to:  This statement has been criticized because the default install contains few running services, and many use cases require additional services. Also, because the ports tree contains unaudited third-party software, it is easy for users to compromise security by installing or improperly configuring packages. However, the project maintains that the slogan is "intended" to refer to a default install and that it is correct by that measure.  One of the fundamental ideas behind OpenBSD is a drive for systems to be simple, clean, and secure by default. The default install is quite minimal, which the project states is to ensure novice users "do not need to become security experts overnight", which fits with open-source and code auditing practices considered important elements of a security system.

Alleged backdoor.

On 11 December 2010, Gregory Perry, a former technical consultant for the Federal Bureau of Investigation (FBI), emailed De Raadt alleging that the FBI had paid some OpenBSD ex-developers 10 years prior to insert backdoors into the OpenBSD Cryptographic Framework. De Raadt made the email public on 14 December by forwarding it to the openbsd-tech mailing list and suggested an audit of the IPsec codebase. De Raadt's response was skeptical of the report and he invited all developers to independently review the relevant code. In the weeks that followed, bugs were fixed but no evidence of backdoors was found. De Raadt stated "I believe that NetSec was probably contracted to write backdoors as alleged. If those were written, I don't believe they made it into our tree. They might have been deployed as their own product."

Criticisms.

In December 2017, Ilja van Sprundel, director at IOActive, gave a talk at the CCC as well as DEF CON, entitled "Are all BSDs created equally? — A survey of BSD kernel vulnerabilities.", in which he stated that albeit OpenBSD was the clear winner of the *BSD in terms of security, "Bugs are still easy to find in those kernels, even in OpenBSD".  Two years later, in 2019, a talk named "A systematic evaluation of OpenBSD’s mitigations" was given at the CCC, arguing that while OpenBSD has some effective mitigations, a significant part of them are "useless at best and based on pure luck and superstition", arguing for a more rational approach when it comes to designing them.

Subprojects.

Many open source projects started as components of OpenBSD, including: Some subsystems have been integrated into other BSD operating systems, and many are available as packages for use in other Unix-like systems.  Linux administrator Carlos Fenollosa commented on moving from Linux to OpenBSD that the system is faithful to the Unix philosophy of small, simple tools that work together well: "Some base components are not as feature-rich, on purpose. Since 99% of the servers don't need the flexibility of Apache, OpenBSD's httpd will work fine, be more secure, and probably faster". He characterized the developer community's attitude to components as: "When the community decides that some module sucks, they develop a new one from scratch. OpenBSD has its own NTPd, SMTPd and, more recently, HTTPd. They work great". As a result, OpenBSD is relatively prolific in creating components that become widely reused by other systems.  OpenBSD runs nearly all of its standard daemons within chroot and privsep security structures by default, as part of hardening the base system.  The Calgary Internet Exchange was formed in 2012, in part to serve the needs of the OpenBSD project.

Third-party components.

OpenBSD includes a number of third-party components, many with OpenBSD-specific patches, such as X.Org, Clang (the default compiler on several architectures), GCC, Perl, NSD, Unbound, ncurses, GNU binutils, GDB, and AWK.

Development.

Development is continuous, and team management is open and tiered. Anyone with appropriate skills may contribute, with commit rights being awarded on merit and De Raadt acting as coordinator. Two official releases are made per year, with the version number incremented by 0.1, and these are each supported for twelve months (two release cycles). Snapshot releases are also available at frequent intervals.  Maintenance patches for supported releases may be applied manually or by updating the system against the patch branch of the CVS repository for that release. Alternatively, a system administrator may opt to upgrade using a snapshot release and then regularly update the system against the branch of the CVS repository, in order to gain pre-release access to recently added features.  The generic OpenBSD kernel provided by default is strongly recommended for end users, in contrast to operating systems that recommend user kernel customization.  Packages outside the base system are maintained by CVS through a ports tree and are the responsibility of the individual maintainers, known as porters. As well as keeping the current branch up to date, porters are expected to apply appropriate bug-fixes and maintenance fixes to branches of their package for OpenBSD's supported releases. Ports are generally not subject to the same continuous auditing as the base system due to lack of manpower.  Binary packages are built centrally from the ports tree for each architecture. This process is applied for the current version, for each supported release, and for each snapshot. Administrators are recommended to use the package mechanism rather than build the package from the ports tree, unless they need to perform their own source changes.  OpenBSD's developers regularly meet at special events called hackathons, where they "sit down and code", emphasizing productivity. Most new releases include a song.

Open source and open documentation.

OpenBSD is known for its high-quality documentation, considered the best among the BSD operating systems, all of which emphasize correct documentation.  When OpenBSD was created, De Raadt decided that the source code should be available for anyone to read. At the time, a small team of developers generally had access to a project's source code. Chuck Cranor and De Raadt concluded this practice was "counter to the open source philosophy" and inconvenient to potential contributors. Together, Cranor and De Raadt set up the first public, anonymous CVS server. De Raadt's decision allowed users to "take a more active role", and established the project's commitment to open access.  OpenBSD does not include closed source binary drivers in the source tree, nor do they include code requiring the signing of non-disclosure agreements.  Since OpenBSD is based in Canada, no United States export restrictions on cryptography apply, allowing the distribution to make full use of modern algorithms for encryption. For example, the swap space is divided into small sections and each section is encrypted with its own key, ensuring that sensitive data does not leak into an insecure part of the system.  OpenBSD randomizes various behaviors of applications, making them less predictable and thus more difficult to attack. For example, PIDs are created and associated randomly to processes; the codice_5 system call uses random port numbers; files are created with random inode numbers; and IP datagrams have random identifiers. This approach also helps expose bugs in the kernel and in user space programs.  The OpenBSD policy on openness extends to hardware documentation: in the slides for a December 2006 presentation, De Raadt explained that without it "developers often make mistakes writing drivers", and pointed out that "the [oh my god, I got it to work] rush is harder to achieve, and some developers just give up." He went on to say that vendor-supplied binary drivers are unacceptable for inclusion in OpenBSD, that they have "no trust of vendor binaries running in our kernel" and that there is "no way to fix [them]... when they break."

Licensing.

OpenBSD maintains a strict license policy, preferring the ISC license and other variants of the BSD license. The project attempts to "maintain the spirit of the original Berkeley Unix copyrights," which permitted a "relatively un-encumbered Unix source distribution." The widely used Apache License and GNU General Public License are considered overly restrictive.  In June 2001, triggered by concerns over Darren Reed's modification of IPFilter's license wording, a systematic license audit of the OpenBSD ports and source trees was undertaken. Code in more than a hundred files throughout the system was found to be unlicensed, ambiguously licensed or in use against the terms of the license. To ensure that all licenses were properly adhered to, an attempt was made to contact all the relevant copyright holders: some pieces of code were removed, many were replaced, and others, such as the multicast routing tools and, were relicensed so that OpenBSD could continue to use them. Also removed during this audit was all software produced by Daniel J. Bernstein. At the time, Bernstein requested that all modified versions of his code be approved by him prior to redistribution, a requirement to which OpenBSD developers were unwilling to devote time or effort.  Because of licensing concerns, the OpenBSD team has reimplemented software from scratch or adopted suitable existing software. For example, OpenBSD developers created the PF packet filter after unacceptable restrictions were imposed on IPFilter. PF first appeared in OpenBSD 3.0 and is now available in many other operating systems. OpenBSD developers have also replaced GPL-licensed tools (such as CVS, diff, grep and pkg-config) with permissively licensed equivalents.

Funding.

Although the operating system and its portable components are used in commercial products, De Raadt says that little of the funding for the project comes from the industry: "traditionally all our funding has come from user donations and users buying our CDs (our other products don't really make us much money). Obviously, that has not been a lot of money."  For a two-year period in the early 2000s, the project received funding from DARPA, which "paid the salaries of 5 people to work completely full-time, bought about $30k in hardware, and paid for 3 hackathons", from the POSSE project.  In 2006, the OpenBSD project experienced financial difficulties. The Mozilla Foundation and GoDaddy are among the organizations that helped OpenBSD to survive. However, De Raadt expressed concern about the asymmetry of funding: "I think that contributions should have come first from the vendors, secondly from the corporate users, and thirdly from individual users. But the response has been almost entirely the opposite, with almost a 15-to-1 dollar ratio in favor of the little people. Thanks a lot, little people!"  On 14 January 2014, Bob Beck issued a request for funding to cover electrical costs. If sustainable funding was not found, Beck suggested the OpenBSD project would shut down. The project soon received a US$20,000 donation from Mircea Popescu, the Romanian creator of the MPEx bitcoin stock exchange, paid in bitcoins. The project raised US$150,000 in response to the appeal, enabling it to pay its bills and securing its short-term future. Since 2014, several large contributions to the OpenBSD Foundation have come from corporations such as Microsoft, Facebook, and Google as well as the Core Infrastructure Initiative.  During the 2016 and 2017 fundraising campaigns, Smartisan, a Chinese company, was the leading financial contributor to the project.

Distribution.

OpenBSD is freely available in various ways: the source can be retrieved by anonymous CVS, and binary releases and development snapshots can be downloaded by FTP, HTTP, and rsync. Prepackaged CD-ROM sets through version 6.0 can be ordered online for a small fee, complete with an assortment of stickers and a copy of the release's theme song. These, with their artwork and other bonuses, have been one of the project's few sources of income, funding hardware, Internet service, and other expenses. Beginning with version 6.1, CD-ROM sets are no longer released.  OpenBSD provides a package management system for easy installation and management of programs which are not part of the base operating system. Packages are binary files which are extracted, managed and removed using the package tools. On OpenBSD, the source of packages is the ports system, a collection of Makefiles and other infrastructure required to create packages. In OpenBSD, the ports and base operating system are developed and released together for each version: this means that the ports or packages released with, for example, 4.6 are not suitable for use with 4.5 and vice versa.

Songs and artwork.

Initially, OpenBSD used a haloed version of the BSD daemon mascot drawn by Erick Green, who was asked by De Raadt to create the logo for the 2.3 and 2.4 versions of OpenBSD. Green planned to create a full daemon, including head and body, but only the head was completed in time for OpenBSD 2.3. The body as well as pitchfork and tail was completed for OpenBSD 2.4. Subsequent releases used variations such as a police daemon by Ty Semaka, but eventually settled on a pufferfish named Puffy. Since then, Puffy has appeared on OpenBSD promotional material and featured in release songs and artwork.  The promotional material of early OpenBSD releases did not have a cohesive theme or design, but later the CD-ROMs, release songs, posters and tee-shirts for each release have been produced with a single style and theme, sometimes contributed to by Ty Semaka of the Plaid Tongued Devils. These have become a part of OpenBSD advocacy, with each release expounding a moral or political point important to the project, often through parody.  Themes have included "Puff the Barbarian" in OpenBSD 3.3, which included an 80s rock song and parody of Conan the Barbarian alluding to open documentation, "The Wizard of OS" in OpenBSD 3.7, related to the project's work on wireless drivers, and "Hackers of the Lost RAID", a parody of Indiana Jones referencing the new RAID tools in OpenBSD 3.8.

OpenBSD is a security-focused, free and open-source, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by forking NetBSD. According to de Raadt, OpenBSD is a research operating system for developing security mitigations.

OpenBSD je otevřený operační systém z rodiny BSD, který vznikl jako fork projektu NetBSD v roce 1995. Jeho autoři kladou důraz na bezpečnost a na software bez děr.


The law.

Every physical body spontaneously and continuously emits electromagnetic radiation and the spectral radiance of a body,, describes the amount of energy it emits at different radiation frequencies. It is the power emitted per unit area of the body, per unit solid angle of emission, per unit frequency. Planck showed that the spectral radiance of a body for frequency at absolute temperature is given by  where is the Boltzmann constant, is the Planck constant, and is the speed of light in the medium, whether material or vacuum. The spectral radiance can also be expressed per unit wavelength instead of per unit frequency. By choosing an appropriate system of unit of measure (i.e. natural Planck units), the law can be simplified to become:  Equating the integral of spectral radiance in per unit wavelength to

Black-body radiation.

A black-body is an idealised object which absorbs and emits all radiation frequencies. Near thermodynamic equilibrium, the emitted radiation is closely described by Planck's law and because of its dependence on temperature, Planck radiation is said to be thermal radiation, such that the higher the temperature of a body the more radiation it emits at every wavelength.  Planck radiation has a maximum intensity at a wavelength that depends on the temperature of the body. For example, at room temperature (~), a body emits thermal radiation that is mostly infrared and invisible. At higher temperatures the amount of infrared radiation increases and can be felt as heat, and more visible radiation is emitted so the body glows visibly red. At higher temperatures, the body is bright yellow or blue-white and emits significant amounts of short wavelength radiation, including ultraviolet and even x-rays. The surface of the sun (~) emits large amounts of both infrared and ultraviolet radiation; its emission is peaked in the visible spectrum. This shift due to temperature is called Wien's displacement law.  Planck radiation is the greatest amount of radiation that any body at thermal equilibrium can emit from its surface, whatever its chemical composition or surface structure. The passage of radiation across an interface between media can be characterized by the emissivity of the interface (the ratio of the actual radiance to the theoretical Planck radiance), usually denoted by the symbol. It is in general dependent on chemical composition and physical structure, on temperature, on the wavelength, on the angle of passage,

Different forms.

Planck's law can be encountered in several forms depending on the conventions and preferences of different scientific fields. The various forms of the law for spectral radiance are summarized in the table below. Forms on the left are most often encountered in experimental fields, while those on the right are most often encountered in theoretical fields.  These distributions represent the spectral radiance of blackbodies—the power emitted from the emitting surface, per unit projected area of emitting surface, per unit solid angle, per spectral unit (frequency, wavelength, wavenumber or their angular equivalents). Since the radiance is isotropic (i.e. independent of direction), the power emitted at an angle to the normal is proportional to the projected area, and therefore to the cosine of that angle as per Lambert's cosine law, and is unpolarized.

Correspondence between spectral variable forms.

Different spectral variables require different corresponding forms of expression of the law. In general, one may not convert between the various forms of Planck's law simply by substituting one variable for another, because this would not take into account that the different forms have different units. Wavelength and frequency units are reciprocal.  Corresponding forms of expression are related because they express one and the same physical fact: for a particular physical spectral increment, a corresponding particular physical energy increment is radiated.  This is so whether it is expressed in terms of an increment

Spectral energy density form.

Planck's law can also be written in terms of the spectral energy

First and second radiation constants.

In the above variants of Planck's law, the "Wavelength" and "Wavenumber" variants use the terms and which comprise physical constants only. Consequently, these terms can be considered as physical constants themselves, and are therefore

Physics.

Planck's law describes the unique and characteristic spectral distribution for electromagnetic radiation in thermodynamic equilibrium, when there is no net flow of matter or energy. Its physics is most easily understood by considering the radiation in a cavity with rigid opaque walls. Motion of the walls can affect the radiation. If the walls are not opaque, then the thermodynamic equilibrium is not isolated. It is of interest to explain how the thermodynamic equilibrium is attained. There are two main cases: (a) when the approach to thermodynamic equilibrium is in the presence of matter, when the walls of the cavity are imperfectly reflective for every wavelength or when the walls are perfectly reflective while the cavity contains a small black body (this was the main case considered by Planck); or (b) when the approach to equilibrium is in the absence of matter, when the walls are perfectly reflective for all wavelengths and the cavity contains no matter. For matter not enclosed in such a cavity, thermal radiation can be approximately explained by appropriate use of Planck's law.  Classical physics led, via the equipartition theorem, to the ultraviolet catastrophe, a prediction that the total blackbody radiation intensity was infinite. If supplemented by the classically unjustifiable assumption that for some reason the radiation is finite, classical thermodynamics provides an account of some aspects of the Planck distribution, such as the Stefan–Boltzmann law, and the Wien displacement law. For the case of the presence of matter, quantum mechanics provides a good account, as found below in the section headed Einstein coefficients. This was the case considered by Einstein, and is nowadays used for quantum optics. For the case of the absence of matter, quantum field theory is necessary, because non-relativistic quantum mechanics with fixed particle numbers does not provide a sufficient account.

Photons.

Quantum theoretical explanation of Planck's law views the radiation as a gas of massless, uncharged, bosonic particles, namely photons, in thermodynamic equilibrium. Photons are viewed as the carriers of the electromagnetic interaction between electrically charged elementary particles. Photon numbers are not conserved. Photons are created or annihilated in the right numbers and with the right energies to fill the cavity with the Planck distribution. For a photon gas in thermodynamic equilibrium, the internal energy density is entirely determined by the temperature; moreover, the pressure is entirely determined by the internal energy density. This is unlike the case of thermodynamic equilibrium for material gases, for which the internal energy is determined not

Kirchhoff's law of thermal radiation.

Kirchhoff's law of thermal radiation is a succinct and brief account of a complicated physical situation. The following is an introductory sketch of that situation, and is very far from being a rigorous physical argument. The purpose here is only to summarize the main physical factors in the situation, and the main conclusions.

Spectral dependence of thermal radiation.

There is a difference between conductive heat transfer and radiative heat transfer. Radiative heat transfer can be filtered to pass only a definite band of radiative frequencies.  It is generally known that the hotter a body becomes the more heat it radiates at every frequency.  In a cavity in an opaque body with rigid walls that are not perfectly reflective at any frequency, in thermodynamic equilibrium, there is only one temperature, and it must be shared in common by the radiation of every frequency.  One may imagine two such cavities, each in its own isolated radiative and thermodynamic equilibrium. One may imagine an optical device that allows radiative heat transfer between the two cavities, filtered to pass only a definite band of radiative frequencies. If the values of the spectral radiances of the radiations in the cavities differ in that frequency band, heat may be expected to pass from the hotter to the colder.

Relation between absorptivity and emissivity.

One may imagine a small homogeneous spherical material body labeled at a temperature, lying in a radiation field within a large cavity with walls of material labeled at a temperature. The body emits its own thermal radiation. At a particular frequency, the radiation emitted from a particular cross-section through the centre of in one sense in a direction normal to that cross-section may be denoted, characteristically for the material of. At that frequency, the radiative power from the walls into that cross-section in the opposite sense in that direction may be denoted, for the wall temperature. For the material of, defining the absorptivity as the fraction of that incident radiation absorbed by, that incident energy is absorbed at a rate.  The rate of accumulation of energy in one sense into the cross-section of the body can then be expressed  Kirchhoff's seminal insight, mentioned just above, was that, at thermodynamic equilibrium at temperature, there exists a unique universal radiative distribution, nowadays denoted, that is independent of the chemical characteristics of the materials and, that leads to a very valuable understanding of the radiative exchange equilibrium of any body at all, as follows.

Black body.

In physics, one considers an ideal black body, here labeled, defined as one that completely absorbs all of the electromagnetic radiation falling upon it at every frequency (hence the term "black"). According to Kirchhoff's law of thermal radiation, this entails that, for every frequency, at thermodynamic equilibrium at temperature, one has, so that the thermal radiation from a black body is always equal to the full amount specified by Planck's law. No physical body can emit thermal radiation that exceeds that of a black body, since if it were in equilibrium with a radiation field, it would be emitting more energy than was incident upon it.  Though perfectly black materials do not exist, in practice

Lambert's cosine law.

As explained by Planck, a radiating body has an interior consisting of matter, and an interface with its contiguous neighbouring material medium, which is usually the medium from within which the radiation from the surface of the body is observed. The interface is not composed of physical matter but is a theoretical conception, a mathematical two-dimensional surface, a joint property of the two contiguous media, strictly speaking belonging to neither separately. Such an interface can neither absorb nor emit, because it is not composed of physical matter; but it is the site of reflection and transmission of radiation, because it is a surface of discontinuity of optical properties. The reflection and transmission of radiation at the interface obey the Stokes–Helmholtz reciprocity principle.  At any point in the interior of a black body located inside a cavity in thermodynamic equilibrium at temperature the radiation is homogeneous, isotropic and unpolarized. A black body absorbs all and reflects none of the electromagnetic radiation incident upon it. According to the Helmholtz reciprocity principle, radiation from the

Stefan–Boltzmann law.

The total power emitted per unit area at the surface of a black body () may be found by integrating the black body spectral flux found from Lambert's

Radiative transfer.

The equation of radiative transfer describes the way in which radiation is affected as it travels through a material medium. For the special case in which the material medium is in thermodynamic equilibrium in the neighborhood of a point in the medium, Planck's law is of special importance.  For simplicity, we can consider the linear steady state, without scattering. The equation of radiative transfer states that for a beam of light going through a small distance, energy is conserved: The change in the (spectral) radiance of that beam () is equal to the amount removed by the material medium plus the amount gained from the material medium. If the radiation field is in equilibrium with the material medium, these two contributions will be equal. The material medium will have a certain emission coefficient and absorption coefficient.  The absorption coefficient is the fractional change in the intensity of the light beam as it travels the distance, and has units of length. It is

Einstein coefficients.

The principle of detailed balance states that, at thermodynamic equilibrium, each elementary process is equilibrated by its reverse process.  In 1916, Albert Einstein applied this principle on an atomic level to the case of an atom radiating and absorbing radiation due to transitions between two particular energy levels, giving a deeper insight into the equation of radiative transfer and Kirchhoff's law for this type of radiation. If level 1 is the lower energy level with energy, and level 2 is the upper energy level with energy, then the frequency of the radiation radiated or absorbed will be determined by Bohr's frequency condition:  If and are the number densities of the atom in states 1 and 2 respectively, then the rate of change of these densities in time will be due to three processes:  where is

Properties.

Peaks.

The distributions,, and peak at a photon energy of  where is the Lambert W function and is Euler's number.  The distributions and however, peak at a different energy  The reason for this is that, as mentioned above, one cannot go from (for example) to simply by substituting by. In addition, one must

Approximations.

In the limit of low frequencies (i.e. long wavelengths), Planck's law becomes the Rayleigh–Jeans law  The radiance increases as the square of the frequency, illustrating the ultraviolet catastrophe. In the

Percentiles.

Wien's displacement law in its stronger form states that the shape of Planck's law is independent of temperature. It is therefore possible to list the percentile points of the total radiation as well as the peaks for wavelength and frequency, in a form which gives the wavelength when divided by temperature. The second row of the following table lists the corresponding values of, that is, those values of for which the wavelength is micrometers at the radiance percentile point given by the corresponding entry in the first row.  That is, 0.01% of the radiation is

Derivation.

Consider a cube of side with conducting walls filled with electromagnetic radiation in thermal equilibrium at temperature. If there is a small hole in one of the walls, the radiation emitted from the hole will be characteristic of a perfect black body. We will first calculate the spectral energy density within the cavity and then determine the spectral radiance of the emitted radiation.  At the walls of the cube, the parallel component of the electric field and the orthogonal component of the magnetic field must vanish. Analogous to the wave function of a particle in a box, one finds that the fields are superpositions of periodic functions. The three wavelengths,, and, in the three directions orthogonal to the walls can be:  where the are positive integers. For each set of integers there are two linearly independent solutions (known as modes). According to quantum theory, the energy levels of a mode are given by:  The quantum number can be interpreted as the number of photons in the mode. The two modes for each set of correspond to the two polarization states of the photon which has a spin of 1. For the energy of the mode is not zero. This vacuum energy of the electromagnetic field is responsible for the Casimir effect. In the following we will calculate the internal energy of the box at absolute temperature.  According to statistical mechanics, the equilibrium probability distribution over the energy levels of a particular mode is given by:  Here  The denominator, is the partition function of a single mode and makes properly normalized:  Here we have implicitly defined  which is the energy of a single photon. As explained here, the average energy in a mode can be expressed in terms of the partition function:  This formula, apart from the first vacuum energy term, is a special case of the general formula for particles obeying Bose–Einstein statistics. Since there is no restriction on the

History.

Balfour Stewart.

In 1858, Balfour Stewart described his experiments on the thermal radiative emissive and absorptive powers of polished plates of various substances, compared with the powers of lamp-black surfaces, at the same temperature. Stewart chose lamp-black surfaces as his reference because of various previous experimental findings, especially those of Pierre Prevost and of John Leslie. He wrote "Lamp-black, which absorbs all the rays that fall upon it, and therefore possesses the greatest possible absorbing power, will possess also the greatest possible radiating power."  Stewart measured radiated power with a thermo-pile and sensitive galvanometer read with a microscope. He was concerned with selective thermal radiation, which he investigated with plates of substances that radiated and absorbed selectively for different qualities of radiation rather than maximally for all qualities of radiation. He discussed the experiments in terms of rays which could be reflected and refracted, and which obeyed the Helmholtz reciprocity principle (though he did not use an eponym for it). He did not in this paper mention that the qualities of the rays might be described by their wavelengths, nor did he use spectrally resolving apparatus

Gustav Kirchhoff.

In 1859, not knowing of Stewart's work, Gustav Robert Kirchhoff reported the coincidence of the wavelengths of spectrally resolved lines of absorption and of emission of visible light. Importantly for thermal physics, he also observed that bright lines or dark lines were apparent depending on the temperature difference between emitter and absorber.  Kirchhoff then went on to consider bodies that emit and absorb heat radiation, in an opaque enclosure or cavity, in equilibrium at temperature.  Here is used a notation different from Kirchhoff's. Here, the emitting power denotes a dimensioned quantity, the total radiation emitted by a body labeled by index at temperature. The total absorption ratio of that body is dimensionless, the ratio of absorbed to incident radiation in the cavity at temperature. (In contrast with Balfour Stewart's, Kirchhoff's definition of his absorption ratio did not refer in particular to a lamp-black surface as the source of the incident radiation.) Thus the ratio of emitting power to absorption ratio is a dimensioned quantity, with the dimensions of emitting power, because is dimensionless. Also here the wavelength-specific emitting power of the body at temperature is denoted by and the wavelength-specific absorption ratio by. Again, the ratio of emitting power to absorption ratio is a dimensioned quantity, with the dimensions of emitting power.  In a second report made in 1859, Kirchhoff announced a new general principle or law for which he offered a theoretical and mathematical proof, though he did not offer quantitative measurements of radiation powers. His theoretical proof was and still is considered by some writers to be invalid. His principle, however, has endured: it was that for heat rays of the same wavelength, in equilibrium at a given temperature, the wavelength-specific ratio of emitting power to absorption ratio has one and the same common value for all bodies that emit and absorb at that wavelength. In symbols, the law stated that the wavelength-specific ratio has one and the same value for all bodies, that is for all values of index. In this report there was no mention of black bodies.  In 1860, still not knowing of Stewart's measurements for selected qualities of radiation, Kirchhoff pointed out that it was long established experimentally that for total heat radiation, of unselected quality, emitted and absorbed by a body in equilibrium, the dimensioned total radiation ratio, has one and the same value common to all bodies, that is, for every value of the material index. Again without measurements of radiative powers or other new experimental data, Kirchhoff then offered a fresh theoretical proof of his new principle of the universality of the value of the wavelength-specific ratio at

Empirical and theoretical ingredients for the scientific induction of Planck's law.

In 1860, Kirchhoff predicted experimental difficulties for the empirical determination of the function that described the dependence of the black-body spectrum as a function only of temperature and wavelength. And so it turned out. It took some forty years of development of improved methods of measurement of electromagnetic radiation to get a reliable result.  In 1865, John Tyndall described radiation from electrically heated filaments and from carbon arcs as visible and invisible. Tyndall spectrally decomposed the radiation by use of a rock salt prism, which passed heat as well as visible rays, and measured the radiation intensity by means of a thermopile.  In 1880, André-Prosper-Paul Crova published a diagram of the three-dimensional appearance of the graph of the strength of thermal radiation as a function of wavelength and temperature. He determined the spectral variable by use of prisms. He analyzed the surface through what he called "isothermal" curves, sections for a single temperature, with a spectral variable on the abscissa and a power variable on the ordinate. He put smooth curves through his experimental data points. They had one peak at a spectral value characteristic for the temperature, and fell either side of it towards the horizontal axis. Such spectral sections are widely shown even today.  In a series of papers from 1881 to 1886, Langley reported measurements of the spectrum of heat radiation, using

Planck's views before the empirical facts led him to find his eventual law.

Planck first turned his attention to the problem of black-body radiation in 1897. Theoretical and empirical progress enabled Lummer and Pringsheim to write in 1899 that available experimental

Finding the empirical law.

Max Planck produced his law on 19 October 1900 as an improvement upon the Wien approximation, published in 1896 by Wilhelm Wien, which fit the experimental data at short wavelengths (high frequencies) but deviated from it at long wavelengths (low frequencies). In June 1900, based on heuristic theoretical considerations, Rayleigh had suggested a formula that he proposed might be checked experimentally. The suggestion was that the Stewart–Kirchhoff universal function might be of the form. This was not the celebrated Rayleigh–Jeans formula, which did not emerge until 1905, though it did reduce to the latter for long wavelengths, which are the relevant ones here. According to Klein, one may speculate that it is likely that Planck had seen this suggestion though he did not mention it in his papers of 1900 and 1901. Planck would have been aware of various other proposed formulas which had been offered. On 7 October 1900,

Trying to find a physical explanation of the law.

Once Planck had discovered the empirically fitting function, he constructed a physical derivation of this law. His thinking revolved around entropy rather than being directly about temperature. Planck considered a cavity with perfectly reflective walls; the cavity contained finitely many hypothetical well separated and recognizable but identically constituted, of definite magnitude, resonant oscillatory bodies, several such oscillators at each of finitely many characteristic frequencies. The hypothetical oscillators were for Planck purely imaginary theoretical investigative probes, and he said of them that such oscillators do not need to "really exist somewhere in nature, provided their existence and their properties are consistent with the laws of thermodynamics and electrodynamics.". Planck did not attribute any definite physical significance to his hypothesis of resonant oscillators, but rather proposed it as a mathematical device that enabled him to derive a single expression for the black body spectrum that matched the empirical data at all wavelengths. He tentatively mentioned the possible connection of such oscillators with atoms. In a sense, the oscillators corresponded to Planck's speck of carbon; the size of the speck could be small regardless of the size of the cavity, provided the speck effectively transduced energy between radiative wavelength modes.  Partly following a heuristic method of calculation pioneered by Boltzmann for gas molecules, Planck considered the possible ways of distributing electromagnetic energy over the different modes of his hypothetical charged material oscillators. This acceptance of the probabilistic approach, following Boltzmann, for Planck was a radical change from his former position, which till then had deliberately opposed such thinking proposed by Boltzmann. Heuristically, Boltzmann had distributed the energy in arbitrary merely mathematical quanta, which he had proceeded to make tend to zero in magnitude, because the finite magnitude had served only to allow definite counting for the sake of mathematical calculation of probabilities, and had no physical significance. Referring to a new universal constant of nature,

Subsequent events.

It was not until five years after Planck made his heuristic assumption of abstract elements of energy or of action that Albert Einstein conceived of really existing quanta of light in 1905 as a revolutionary explanation of black-body radiation, of photoluminescence, of the photoelectric effect, and of the ionization of gases by ultraviolet light. In 1905, "Einstein believed that Planck's theory could not be made to agree with the idea of light quanta, a mistake he corrected in 1906." Contrary to Planck's beliefs of the time, Einstein proposed a model and formula whereby light was emitted, absorbed, and propagated in free space in energy quanta localized in points of space. As an introduction to his reasoning, Einstein recapitulated Planck's model of hypothetical resonant material electric oscillators as sources and sinks of radiation, but then he offered a new argument, disconnected from that model, but partly based on a thermodynamic argument of Wien, in which Planck's formula played no role. Einstein gave the energy content of such quanta in the form. Thus Einstein was contradicting the undulatory theory of light held by Planck. In 1910, criticizing a manuscript sent to him by Planck, knowing that Planck was a steady supporter of Einstein's theory of special relativity, Einstein wrote to Planck: "To me it seems absurd to have energy continuously distributed in space without assuming an aether."  According to Thomas Kuhn, it was not till 1908 that Planck more or less accepted part of Einstein's arguments for physical as distinct from abstract mathematical discreteness in thermal radiation physics. Still in 1908, considering Einstein's proposal of quantal propagation, Planck opined that such a revolutionary step was perhaps unnecessary. Until then, Planck had been consistent in thinking that discreteness of action quanta was to be found neither in his resonant oscillators nor in the propagation of thermal radiation. Kuhn wrote that, in Planck's earlier papers and in his 1906 monograph, there is no "mention of discontinuity, [nor] of talk of a restriction on oscillator energy, [nor of] any formula like." Kuhn pointed out that his study of Planck's papers of 1900 and 1901, and of his monograph of 1906, had led him to "heretical" conclusions, contrary to the widespread assumptions of others who saw Planck's writing only from the perspective of later, anachronistic, viewpoints. Kuhn's conclusions, finding a period till 1908, when Planck consistently held his 'first theory', have been accepted by other historians.  In the second edition of his monograph, in 1912, Planck sustained his dissent from Einstein's proposal of light quanta. He proposed in some detail that absorption of light by his virtual material resonators might be continuous, occurring at a constant rate in equilibrium, as distinct from quantal absorption. Only emission was quantal. This has at times been called Planck's "second theory".  It was not till 1919 that Planck

Planck's law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature "T", when there is no net flow of matter or energy between the body and its environment.

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