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166 [253] DESAGULIERS FAHRENHEIT
ion that it proved convenient to divide the volume change between the freezing point and boiling point of water into eighty divisions. On the Reaumur scale, then, the freezing point of water is 0° and the boiling point is 80°. For a while the Reaumur scale held its own against the superior thermometers of Fahrenheit and of Celsius [271], but slowly it lost ground and is now virtually out of use. Reaumur’s most significant work was on the process of digestion. For a cen tury scholars had been divided on the question of whether digestion was a me chanical process, a sort of grinding as Borelli [191] had held, or a chemical process, a sort of fermentation, as Syl vius [196] supposed. Reaumur devised an experiment that settled the matter. In 1752 he experimented with a hawk. He placed meat in small metal cylinders open at both ends, the ends being cov ered by wire gauze, and persuaded the hawk to swallow them. Ordinarily a hawk swallows its food in large pieces, digests what it can, and regurgitates the remainder. Reaumur waited for the hawk to regurgitate the cylinders and found the meat partially dissolved. He concluded that the meat could not have been affected by grinding or by any mechanical action since the metal cylin der protected it from that. Therefore the stomach juices must have had a chemical action on the meat. He checked this by collecting a quan tity of the stomach juice by allowing the hawk to swallow a sponge and, after re gurgitation, squeezing the juice out. This fluid, he found, did indeed slowly dis solve meat placed in it. He experimented with dogs, too, and obtained the same results. Digestion, then, is a chemical process and no one has had occasion to doubt this in the two centuries since Reaumur’s time. [253] DESAGULIERS, John Théophile French-English physicist
March 12, 1683 Died: London, England, March 10, 1744 La Rochelle had been the center of French Protestantism in the seventeenth century. It had been taken by the French Catholic monarchy under the guidance of Richelieu in 1628, but it was not till 1685 that the repressive attitude of Louis XIV made life entirely impossible for the Protestants. In that year, Desaguliers’ family, who were Protestants, fled to England and there they remained. Desaguliers was educated at Oxford, was ordained a deacon in 1710, and even served as chaplain to Frederick, Prince of Wales. (He never reigned him self, but he was the father of George HI.) Desaguliers was an ardent experi menter in many fields and a strong expo nent of the Newtonian point of view. He was particularly interested in electricity and repeated and extended the experi ments of Stephen Gray [262] in that field. It was he who first used the word “conductor” to describe those substances that could conduct a flow of electricity. Nonconductors he called “insulators” from the Latin word for “island” since nonconductors could pen up the electric fluid as the sea penned up an island. [254] FAHRENHEIT, Gabriel Daniel (fah'ren-hite) German-Dutch physicist
land), May 24, 1686 Died: The Hague, Netherlands, September 16, 1736 In 1701 Fahrenheit, the son of a wealthy merchant, emigrated to Amster dam after the sudden death of both par ents; there he became a manufacturer of meteorological instruments. Obviously one of the chief devices that can be used for studying climate is a thermometer. The thermometers of the seventeenth century, however, such as the gas ther mometer of Galileo [166] or of Amon tons [244], were insufficiently exact for the purpose. Fluid thermometers had come into use, but they used either alcohol or alco- 167 [254] FAHRENHEIT DELISLE
hol-water mixtures. Alcohol alone boiled at too low a temperature to allow high temperatures to be measured, and alco hol-water mixtures, which did a bit bet ter in this respect, changed volume with changing temperature in too uneven a way.
In 1714 Fahrenheit made the key ad vance of substituting mercury for alco hol. He made this practical by inventing a new method for cleaning mercury so that it wouldn’t stick to the walls of the narrow tube of the thermometer. The use of mercury meant that temperatures well above the boiling point of water as well as below its freezing point could be recorded. In addition, mercury expanded and contracted at a more constant rate than most other substances and a mer cury thermometer could be marked off more accurately into finer subdivisions. In 1701, for instance, Newton [231] had suggested that the temperature of freezing water and of the body be used as fixed points on the thermometer scale and that the difference in fluid level at these points be marked off into twelve equal divisions. Fahrenheit, however, added salt to water to get the lowest freezing point he could and called that zero. (He wanted to avoid negative temperatures on winter days that were well below the freezing point of pure water.) He then divided the difference in level between that point and that reached at body temperature not into twelve parts but into eight times that many (in line with the high preci sion of his instrument) or ninety-six “de grees.” He later adjusted that slightly in order to make the boiling point of water come out to 212°, exactly 180 degrees above the freezing point of pure water, set at 32°. On this Fahrenheit scale, body temperature is 98.6°. This was the first really accurate ther mometer, and Fahrenheit used it to ex pand Amontons’ finding that the boiling point of water was fixed. He checked other liquids and found that each had a fixed and characteristic boiling point under ordinary conditions. He also no ticed that this boiling point changed with changes in pressure. Fahrenheit’s report on his thermom eter in 1724 earned him election that year to the Royal Society. The Fahren heit scale was adopted at once in Great Britain and the Netherlands. Most of the civilized world, and sci entists everywhere, however, use the scale invented by Celsius [271] a quar ter century after Fahrenheit’s first mer cury thermometer. [255] DELISLE, Joseph Nicolas (duh- leel') French astronomer Born: Paris, April 4, 1688 Died: Paris, September 11, 1768 Delisle was the ninth child of a histo rian and geographer. He was educated at the Collège Mazarin, with no antici pation of a scientific career, but a solar eclipse in 1706 imbued him with a fasci nation for astronomy. He began studying it avidly and found work, almost any work, to do at the Paris Observatory. He showed enough talent to get a professorial appointment at the Collège Royal in 1718. Then Peter I (the Great) of Russia, who was anxious to modern ize Russia in his own lifetime, felt the need of a modem astronomical observa tory in the land and invited Delisle to do the job. In 1725 Delisle was in St. Petersburg to see what he could do in four years and, as it turned out, he stayed twenty-two years. In the process, though, he established the observatory and trained a whole generation of as tronomers so that while Russia remained backward in some branches of science, she developed an astronomical tradition equal to that in western Europe. He re turned to Paris in 1747. He was the first astronomer to take seriously the possibility of utilizing a transit of Venus as a way of determining the scale of distances in the solar system. In 1761, the year of such a transit he or ganized a worldwide study of the phe nomenon, the first such to be attempted. It was the prelude for more serious and sophisticated efforts in the next century. 168 [256] GOLDBACH
BRADLEY [258] [256] GOLDBACH, Christian (gold+ahkh) German-Russian mathematician Born: Königsberg, Prussia (now Kaliningrad, Soviet Union), March 18, 1690
ber 20, 1764 Goldbach, the son of a minister, stud ied medicine and mathematics at the University of Königsberg. In 1710, he made a grand tour of Europe (a com mon way of attaining an education for those who could manage it). In 1725, he settled down in Russia, becoming profes sor of mathematics at the Imperial Acad emy of St. Petersburg; in 1728 he served as tutor to the short-lived Peter II (grandson of Peter the Great). Goldbach is most famous in mathe matics for “Goldbach’s conjecture,” something Goldbach mentioned in 1742 in a letter to Euler [275]. (Goldbach was a voluminous correspondent with the mathematicians of the time.) The conjecture is this: “Every even number greater than 2 can be expressed as the sum of two prime numbers.” Thus 4 = 2 + 2; 6 = 3 + 3; 8 = 3 + 5; 10 = 3 + 7; 12 = 5 + 7; and so on. Mathematicians have found it to be true by actual testing for all even numbers up to 10,000 and for some beyond; and no one really expects to find any exceptions. The catch is, though, that in over two centuries, no mathematician has man aged to prove his conjecture. How can something so simple and so apparently true avoid proof? It is one of the frustra tions of mathematics. [257] MUSSCHENBROEK, Pieter van (mois'en-brook) Dutch physicist
Musschenbroek was born into a family of instrument makers who by the time of his birth had turned to the manufacture of scientific instruments such as tele scopes, microscopes, and air pumps. Pieter studied at the University of Lei den and received his medical degree in 1715, and a Ph.D. in 1719. From 1721, he held professorial positions first at Duisberg, then at Utrecht, and finally at Leiden.
Musschenbroek is most famous for his invention of the first truly efficient device for storing static energy. Until then, there were such things as the sulfur ball of Guericke [189] which could be charged with enough electricity to pro duce interesting phenomena, but not with enough to be truly startling. Musschenbroek, however, placed water in a metal container suspended by in sulating silk cords and led a brass wire through a cork into the water. He built up a charge in the water but had not the slightest idea of how great a charge until an assistant happened to pick up the container and then touch the brass wire outside the cork. The container promptly discharged through the assistant’s body and gave him a fearful shock; the first good-sized artificial electric shock any one had ever received. (The lightning stroke is a natural one, of course.) This happened at the University of Leiden, also spelled Leyden, in January 1746. The news spread rapidly and soon “Leyden jars” were being prepared and improved everywhere. For the first time, physicists had a way of preparing an in tense electric charge and studying its properties. Within six years, Franklin [272] was to make astonishing use of it. [258] BRADLEY, James English astronomer
March 1693 Died: Chalford, Gloucestershire, July 13, 1762 Bradley was educated at Oxford and received his master’s degree in 1717. He was introduced to astronomy through the interest taken in him by his uncle, the Reverend James Pound, himself an as tronomer. The young man’s aptitude in mathematics gained him the friendship
[258] BRADLEY
BRADLEY [258] of Newton [231] and Halley [238] and he was elected to the Royal Society in 1718. Not really expecting to make a liv ing as an astronomer, he became a vicar in the Church of England in 1719 but resigned in 1721 in order to teach at Ox ford. As it happened, astronomy sup ported him the rest of his life, though he labored hard in return. His major astronomical concern was to measure the parallax of the stars. When Copernicus [127] first suggested that the earth moved about the sun, it seemed inevitable that because of this motion the nearer stars would be dis placed—compared with the more distant ones—because they would be viewed at varying angles as the earth moved. No such parallax was, in fact, observed. Co pernicus declared this was because the stars were so distant that the parallax was too small to measure. His opponents said that the parallax was not observed because the earth was not moving. Al though by Bradley’s time the Copemican position was accepted by all astrono mers, it would still have been satisfying to measure the parallax and obtain some idea of the distance of the stars that was more exact than the phrase “very dis tant.”
Bradley’s close observations, with a telescope 212 feet long, did, indeed, indi cate to him that the stars showed a tiny displacement through the year, moving in a small ellipse. However, the motion did not jibe with the earth’s motion in exactly the way expected of a parallactic displacement. It was not until 1728 that the true explanation occurred to him, during a boat ride on the Thames River when he noticed the wind vane on the mast shift direction whenever the boat put about. The usual explanation advanced to ac count for Bradley’s effect, however, in volves the rain. If rain falls vertically, a man holds an umbrella directly over his head. If he walks he must angle the um brella in the direction in which he walks. The faster he walks the more he must angle the umbrella. In the same way, to observe light from a moving earth the telescope must be angled very slightly. The angling of the telescope makes the star appear in a slightly different position as the year moves on. From the amount of angling, the amount of the “aberration of light,” it was possible for Bradley to tell the ratio between the velocity of the earth about the sun and the velocity of light. In this way he was able to produce a second method of estimating the velocity of light, which had first been reported by Roemer [232] a half century before. He succeeded in confirming Roemer’s re sults and rescuing them from oblivion, although Bradley’s figure was the more accurate and very much like the cur rently accepted value for the velocity of light. To be sure, Bradley did not detect the parallax of the stars and could not tell how distant they were. That had to wait for Bessel [439] a century afterward. However, his main purpose was solved. Light would not undergo aberration if the earth were not moving, and his dis covery was the first direct evidence that the earth was not at rest and that Coper nicus’ view was more than merely a mat ter of simplifying the basis of calcula tions. The phenomenon of aberration also tended to support the Newtonian theory of light as a shower of particles (like rain). In his careful positioning of stars Brad ley also discovered that the earth’s axis underwent small periodic shifts, which he called “nutation.” This was due to changes in the direction of the gravita tional attraction of the moon as our sat ellite moved on its rather complicatedly irregular orbit. To detect nutation Brad ley had to determine differences of two seconds of arc. Since he could not detect stellar parallax, that must involve posi tion shifts that were smaller still. Hence, stars had to be very far off. He didn’t publish his discovery till 1748, testing it first by a careful nineteen-year study of stellar positions. In 1733 he measured the diameter of Jupiter and, for the first time, astrono mers began to realize just how much larger some of the planets were than our own earth—for so long regarded as the massive center of the universe. In 1742, upon the death of Halley, 1 7 0
[259] HARRISON
HARRISON [259] Bradley was appointed the third astrono mer royal and in 1748 he was awarded the Copley medal. He finally managed to get a decent appropriation out of the government and with it bought instru ments. He is supposed to have turned down a salary increase, however, observ ing that if the position of astronomer royal were made too lucrative, astrono mers would not be appointed to it. He devoted himself to preparing a star map that was even more extensive and accurate than that of Flamsteed [234]. He had the same industry and applica tion as Flamsteed, and also the advan tage of being able to correct for the tiny errors introduced by aberrations and nu tation, of which Flamsteed, of course, had been unaware. He strongly supported the adoption of the Gregorian calendar by Great Britain in 1752, a view that brought upon him the displeasure of much of the unthink ingly conservative public. [259] HARRISON, John English instrument maker
24, 1693 Died: London, March 24, 1776 The eighteenth century saw the British government still deeply concerned with the problem of determining longitude at sea, the problem that on the advice of Flamsteed [234] had inspired the found ing of the Greenwich Observatory. One way was for the navigator to know the Greenwich time accurately wherever he might be on the face of the earth. From the difference between Greenwich time and the local time, as established astronomically, the longitude could be calculated. For this, though, an accurate timepiece was needed, and one that could be used on board ship. An or dinary pendulum clock could not, be cause the swaying upset the periodic mo tion of the pendulum. In 1707 a British fleet miscalculating its position came to grief on rocks off Cornwall. In 1713, therefore, the British government offered a series of prizes of up to £20,000 for an accurate ship’s chronometer. A century earlier, in 1598, Philip III of Spain had offered a prize, never claimed, for the same thing. Now, however, the problem was tackled by John Harrison, a Yorkshire mechanic and the son of a carpenter, self-trained and equipped with nothing but an almost supernatural mechanical sense. Beginning in 1728 he built a series of five clocks, each better than the one be fore. Each clock was so mounted that it could take the sway of a ship without being adversely affected. He designed a pendulum of different metals so that temperature changes expanded both metals in such a way as to leave the overall length the same, and the period of beat, in consequence, unaltered. He also inserted a mechanism that allowed the clock to continue to keep time undis turbed while it was being wound. Any one of Harrison’s clocks met the demands of the prize conditions. In fact they were more accurate at sea than any other clock of the time was on land. One of them was off by less than a minute after five months at sea. To be sure, the first four clocks were heavy (one weighed sixty-six pounds) and complicated and expensive, but the conditions of the prize said nothing about size or complexity or expense. The fifth clock, moreover, was no bigger than a large watch and it was even better than the others. However, the British Parliament put on an extraordinary display of meanness in this connection. It wore Harrison out with its continual delays in paying him the money he had earned. It repeatedly demanded ever greater perfection, and although Harrison always met those de mands it would pay him only niggardly sums. Possibly this was because Harrison was a provincial mechanic and not a gentleman of the Royal Society. Finally the young King George III took a personal interest and announced that he himself would serve as Harrison’s counselor—one of the shining acts of that well-intentioned but stubbornly wrongheaded monarch. Harrison finally received his money in 1765. Harrison’s chronometer introduced the modern era of ship navigation and was
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