William Herschel, the German-born, star-gazing musician who effectively doubled the size of the solar system with a single discovery in 1781, was not regarded as a scientist. That word had not been coined during most of the era that will now be known, thanks to Richard Holmes' amazingly ambitious, buoyant new fusion of history, art, science, philosophy and biography, as 'The Age of Wonder.' And Holmes' excitement at fusing long-familiar events and personages into something startlingly new is not unlike the exuberance of the age that animates his groundbreaking book. In Herschel's day (and that of his sister, Caroline, who functioned as his doting assistant to the point of feeding him like a baby bird), science was deductively methodical. And astronomy was no amateur's game. But Herschel charted the skies as if making musical notations. And when he lacked instruments with enough precision, he painstakingly invented a telescope with startling new powers of magnification. Looking through it, he noted a starlike object, twice as far from the Sun as Saturn, that appeared to be moving yet did not have a comet's tail. He identified this as the planet Georgium Sidus, first named for George III of Britain but later known as Uranus. (Holmes is much too spirited a writer to resist making a bon mot about the English pronunciation of that name.) Beyond enlivening the story of Herschel's discovery into a gripping narrative, this book speculates fascinatingly about the ramifications of such a breakthrough. Thanks to Herschel the idea of a fixed universe was challenged, replaced by a cosmos in flux. Was that cause for wonder or terror? What were its theological implications? How would it influence a future generation of poets? (The thrill of this breakthrough would later figure in one of Keats' most famous sonnets, 'On First Looking Into Chapman's Homer.') Where would it figure in the relay race of scientific discoveries? In order to structure his big, sweeping book about such issues, Holmes uses two exploratory voyages as bookends. The first, a trip to Tahiti in 1769 led by Capt. James Cook, brought the eager young botanist Joseph Banks to a place he would regard as a paradise, botanical and otherwise. (Holmes quotes deftly from Banks' delightfully candid journals, noting that Banks wrote with 'gentlemanly jeu d'esprit.') The book then follows Banks back to England, where, at the age of 35, he became president of the Royal Society in 1778. He would hold that post for 41 years and encourage the other young pioneers whose stories Holmes has told. 'The Age of Wonder,' a book with a distinct taste for high times, next moves to the golden age of ballooning, which began as an offshoot of paper-bag manufacturing. Gorgeously illustrated, 'The Age of Wonder' captures the full gaudiness of early French ballooning experiments in Easter-egg-colored airborne specimens. And it finds an element of bawdy comedy in the era's gossipy whisperings about what might happen up in the air. ('So the first Mile High Club was also formed,' Holmes writes of one such story.) A wild anecdote about one American-British collaborative effort says of the two balloonists that 'quite early on, each accidentally managed to drop the other's national flag over the side of the basket and then profusely apologized.' As to the rest of what was spilled overboard, Holmes' attention to detail raises the question of how exactingly such scientific endeavors really need to be documented. But this book also understands the seriousness of these early experiments and the confusion they engendered: Was the eagerness to make a first crossing of the English Channel a sporting, scientific or diplomatic matter? What could balloon flight be used to measure? What would be its legacy? (The first test pilot with 'the right stuff' can be found here.) And why should this kind of story not be told as enthusiastically as stories about artists and historical figures are? Overall 'The Age of Wonder' makes a splendid case for treating the history of science in a bright new way. Much of the book is also devoted to Humphry Davy, whose reputation is multifaceted. He wrote poetry; he had lively friendships with some of the best-known writers of his day; he invented a lamp that would prevent methane gas from exploding and save the lives of countless miners. Best immortalized here, though, are Davy's experiments with nitrous oxide, tests in which he eagerly served as guinea pig. Inhaling that substance gave him 'a thrilling all over me most exquisitely pleasurable,' he recorded. 'I said to myself I was born to benefit the world by my great talents.' That Davy did not benefit the world by realizing surgical patients could be anesthetized is symptomatic, Holmes writes, of the strange, uncharted world that this book explores. Davy knew he was discovering something; what he did not know was what its practical applications might be. And with the kind of throwaway brilliance that makes this book so enthralling, Holmes uses only a footnote to conjure one of science's least documented realms: that of failure. The cliche of the 'Eureka!' moment easily obscures the doubt and uncertainty that are also part of the discovery process. A particularly inspired section of the book relates Mary Shelley's 'Frankenstein' to dissection, to the debate about the existence of a life force, and to the way fiction writers and poets could invoke spiritual power while avoiding making reference to God. But by the time the book reaches the Age of Wonder's concluding event, Charles Darwin's five-year voyage on the Beagle beginning in 1831, it has raised both the antecedents and ramifications of today's most enduring scientific debates, on subjects from global warming to extraterrestrial life to intelligent design. It is impossible to understand where these arguments are headed, 'The Age of Wonder' maintains, without knowing where they began. PUBLICATION NOTES: 'THE AGE OF WONDER: How the Romantic Generation Discovered the Beauty and Terror of Science' By Richard Holmes Illustrated. 552 pages. Pantheon Books. $40. 