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THE REVOLUTIONARY PROFESSOR (4)

Among the books he had acquired as a young man was a copy
of Optica Promota (The Promotion of Optics) by James Gregory, the distinguished Scottish mathematician and astronomer. As was his habit, Newton dog-eared the passages most important to him, including Gregory’s design for the reflecting telescope. As yet, no one had successfully built a working reflector. In 1663 Gregory himself had gone so far as to order a special lens from Richard Reive, London’s leading instrument maker, but Reive had failed in his attempts to produce the delicate object.

Newton took up the challenge a few years later, and his reason for doing so is not difficult to understand. Unlike the refracting telescope, which forms an image of an object with lenses, the reflector contains a parabolic mirror from which all light is reflected at the same angle. The advantage of this design is that the observer is not hindered by chromatic aberration, the hazy, rainbowlike phenomena produced when rays of different wavelengths are not brought to the same focus on passing through a lens. Though no one but Newton realized it at the time, the reflecting telescope, in producing an image free from distortion, offered further support for his theory of light and colors.

With the same skilled hands that had produced the models and clocks of his youth, Newton set to work. Using a thin piece of metal rather than glass, which is almost impossible to grind evenly with hand tools, he created a hollow in the shape of a saucer. He then prepared a special alloy composed of copper, tin, and arsenic, which is white in color and takes a high polish. When this tedious task was completed, he coated the metal mirror, or speculum, and placed it and other components in a small tube. In a letter to an unnamed friend, dated February 23, 1669, he described its performance. Newton calculated that the instrument was capable of magnifying “about 40 times in diameter which is more than any 6 foot tube can do, I believe with distinctness. I have seen with it Jupiter distinctly round and his satellites.” He had no doubt that a carefully crafted six-foot reflector would perform as well as any “60 or 100 foot tube made after the common way.” Realizing howpuzzling this claim might sound, he added, “It may seem a paradoxical assertion, yet it is the necessary consequence of some experiments which I have made concerning the nature of light.”

Word of Newton’s triumph spread to London, where he was erroneously hailed as the inventor of the reflector. This circumstance was reminiscent of 1609, when Galileo constructed the first refracting telescope in Italy from a description sent to him by a scientific correspondent from abroad. Most anxious to see Newton’s telescope were members of the Royal Society, a scientific order founded in 1660 and chartered by none other than King Charles II. The society took as its motto part of the Latin quotation Nullius in verba, which freely translates, “Not by word of mouth.” Its embership, which included the finest scientific minds of the time, both English and foreign, were pledged to the experimental method as opposed to the ancient practice of observation alone. The society’s findings were regularly published in the renowned Philosophical Transactions, which became the model for other scientific journals—even to the present day.

Taken From : Isaac Newton