What familiar device was invented by human-computer interface engineer Douglas Engelbart, creator of hypertext?
Purple Numbers Purple Numbers is a suite of tools that allows one to address paragraphs of HTML content. It was originally conceived by Douglas Engelbart for his creation of hypertext. The name comes from the faint, purple numbers at the end of each paragraph, which represent the link to that paragraph. The name was coined by Christina Engelbart, Doug's daughter.
Telegraph sounder A telegraph sounder is an antique electromechanical device used as a receiver on electrical telegraph lines during the 19th century. It was invented by Alfred Vail after 1850 to replace the previous receiving device, the cumbersome Morse register and was the first practical application of the electromagnet. When a telegraph message comes in it produces an audible "clicking" sound representing the "dots" and "dashes" of Morse code. A telegraph operator would translate the sounds into characters representing the telegraph message.