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201 [307] CAVENDISH DARWIN
in the equation but the earth’s mass would be known and the earth’s mass could be calculated. It was assumed that the gravitational constant was the same for all bodies and that it could, in theory, be determined if only the gravitational attraction between two objects, each of known mass, could be measured. The trick was to measure this attraction, for gravitational force is very weak and it takes a very large body, far too large to work with in a labora tory, to pile up enough of it to measure easily. Cavendish tackled the problem in 1798. Using a method suggested by Michell [294], he performed what is now commonly referred to as the Cavendish experiment. Cavendish suspended a light rod by a wire attached to its center. At each end of the rod was a light lead ball. The rod could twist freely about the wire and a light force applied to the balls would produce such a twist. Cavendish mea sured how large a twist was produced by various small forces. He brought two large balls near the two light balls, one on either side. The force of gravity between the large balls and light ones twisted the wire. From the extent of twist, Cavendish calculated the gravitational force between the two pairs of balls. He knew the distance between them, center to center, and the mass of each. This meant he had all the figures required for Newton’s equadon, except for the gravitational constant, and he could now solve for that. Once the constant was determined, it could be put into the equation represent ing the attraction between the earth and some object of known mass upon its sur face. Again all quantities were known with one exception—the mass of the earth, and now that could be calculated for. The earth turned out to have a mass of 6,600,000,000,000,000,000,000 tons and to have a density of about five and a half times that of water. (Newton with his clear intuition had guessed it might come to that a century before.) The Cavendish Physical Laboratory at Cambridge—which a century after Cav endish’s time was to produce work of unparalleled excellence in nuclear phys ics—is named in his honor. [308] DARWIN, Erasmus English physician Born: Elton, Nottinghamshire, December 12, 1731 Died: Breadsall Priory, near Derby, April 18, 1802 Darwin, the son of a prosperous law yer, studied at Cambridge and obtained his medical degree at the University of Edinburgh in 1754. He was one of the foremost physicians of his day so that George III asked him to become his per sonal physician in London. Darwin, however, refused. He was a man of decided opinions, radical, freethinking, and a prohibi tionist. He was a member of the Lunar Society, as were Watt [316] and Priestley [312], He had the deplorable habit of writing long, didactic poems that had some in terest as far as scientific content was concerned but no discernible poetic value. His early poems dealt largely with botany and in them he backed the classification system introduced by Lin naeus [276]. His second most famous accom plishment is his last book, Zoonomia, written 1794-1796, in which he elabo rated on Buffon’s feelings about evolu tion and anticipated some of the sugges tions of Lamarck [336] on the subject. Darwin argued that evolutionary changes were brought about by the direct influence of the environment on the or ganism. The accomplishment for which he is most famous, however, is his being the grandfather (by his first wife) of Charles Darwin [554], who a little over half a century later was to advance the theory of evolution, which, with necessary modifications, is now believed to be the correct one. In addition Erasmus Darwin became the grandfather (by his second wife) of Francis Galton [636]. Erasmus Darwin’s reputation has suffered partly by his being overshad owed by his more famous grandson and 20? [309] LALANDE
ARKWRIGHT [311] partly by a campaign of ridicule set in motion by the conservative British gov ernment during the French revolutionary era against Darwin and others who sym pathized with the French revolutionaries. [309] LALANDE, Joseph Jérôme Le Français de (la-lahndO French astronomer
11, 1732 Died: Paris, April 4, 1807 Lalande, the son of a post office official, had studied law as a young man, but he happened to lodge near an astro nomical observatory, and this caught his fancy. He completed his legal education, but did not practice. Instead, in 1751 he went to Berlin to take observations on the parallax of the moon, as Lacaille [284] was sent to southern Africa for the purpose. He became professor of astronomy at the Collège de France in 1762 and in 1795 became director of the Paris Obser vatory. In the hectic decade of the 1790s, he was openly anti-Jacobin and did what he could to save some who were threatened by the Reign of Terror. Later, he did not hesitate to indicate his opposition to the war policies of Napo leon Bonaparte. He devoted much of his time to pre paring a catalogue of forty-seven thou sand stars which he published in 1801. One of the stars, listed Lalande 21185, turned out eventually to be the third nearest to the sun and to be one of those which in the mid-twentieth century was discovered by Van de Kamp’s [1247] ob servatory to possess a planet. He was also one of those who observed Neptune and recorded its position (but without realizing it was a planet and not a star) a full half century before its discovery by Leverrier [564], He was a great popularizer of astron omy and wrote all the astronomical arti cles in Diderot’s [286] Encyclopedia. In 1798 he made a balloon ascension and later suggested improvements in the parachute. [310] MASKELYNE, Nevil (masTaih- line) English astronomer Born: London, October 6, 1732 Died: Greenwich, London, Feb ruary 9, 1811 Maskelyne, bom into an upper-class family, graduated from Cambridge Uni versity in 1754 and was ordained as a clergyman in 1755. However, he had done well in mathematics and in science, and an eclipse he had viewed in 1748 had interested him permanently in as tronomy.
Someone was needed to head an expe dition to St. Helena to view the transit of Venus in 1761 and Bradley [258] recom mended Maskelyne. The transit observa tion as a method of determining the dis tance of Venus and, therefore, of other bodies of the solar system, was a failure because of clouds and other problems. On the way there, however, Maskelyne worked on methods of determining lon gitude by lunar observations, and this method competed with that of the use of the chronometer devised by Harrison [259],
Harrison won out for the prize that had been offered, but Maskelyne went on to produce lunar tables and the Nau
navigational aid for well over a century. He was appointed fifth astonomer royal, succeeding Nathaniel Bliss, in 1765. He was the first man to make time measurements that were accurate to a tenth of a second.
English inventor Born: Preston, Lancashire, De cember 23, 1732 Died: Cromford, Derbyshire, Au gust 3, 1792 Arkwright, the youngest of thirteen children, was a barber and wigmaker in his youth. A secret process for dyeing hair was the foundation of his fortune. He had little formal education, but in mechanical invention this is not neces sarily a handicap. By 1769, with help
[312] PRIESTLEY PRIESTLEY
from others and with guidance from the work of previous inventors, he patented a device that would spin thread by me chanically reproducing the motions or dinarily made by the human hand. At first, this was powered by animals, then by falling water, and finally, in 1790, by steam. Arkwright invented (or pro moted) machinery that would replace handwork in other steps of textile manu facture and became the first “capitalist” of the newborn industrial age. The ma chines not only replaced handwork; they produced so rapidly and efficiently that handworkers were permanently out of business. Popular rage against his ma chines put his mills and himself in dan ger more than once, but the progress of mechanization was too obviously profitable for society in general and for a small group of hard-driving men in par ticular. In 1782, Arkwright was employing five thousand men. He was appointed high sheriff of Derbyshire in 1783 and was knighted in 1786. At his death his fortune amounted to two and a half mil lion dollars, an enormous sum for those days.
[312] PRIESTLEY, Joseph English chemist Born: Birstal Fieldhead, Yorkshire, March 13, 1733 Died: Northumberland, Pennsyl vania, February 6, 1804 Priestley’s mother died when he was six and he was brought up by a pious aunt. The boy was slight, rather sickly, and suffered from an impediment in his speech. In his youth he studied lan guages, logic, and philosophy and showed himself a prodigiously good stu dent in all these, learning a variety of languages, including Hebrew and Arabic, rather like Hamilton [545] seventy years later. He never studied science formally, yet it was in science that he made his name. He was the son of a Nonconformist preacher and was himself even more rad ical in religion, despite his aunt’s up bringing, for he eventually became a Unitarian minister. He was radical in politics as well, openly supporting the American colonists when they were re volting against George III. He was also against the slave trade and against reli gious bigotry of all sorts. One of his books seemed radical enough to be officially burned in 1785. It was his sym pathy for the French Revolution that eventually got him into the most serious trouble.
In 1766, on one of his periodic visits to London, Priestley met Benjamin Frank lin [272], who was then in England in a vain attempt to adjust the dispute with the American colonies over taxation. That apparently was what influenced him to take up a scientific career. Shortly after, he took over a pastorate in Leeds; there was a brewery next door, and this was another piece of scientific good fortune. Under Franklin’s in fluence, Priestley did some research on electricity, becoming the first to discover that carbon was an electrical conductor. He then wrote an important history of electrical research in 1769, and later one on the history of optics. He was the first to suggest that electricity would prove of importance to chemistry, and eventually he turned to chemistry itself. Fermenting grain produces a gas, the properties of which Priestley took to studying with interest and curiosity. He noted that it put out flames, was heavier than air, and dissolved to a certain ex tent in water. It was, in fact, carbon dioxide, the “fixed air” of Black [298]. When Priestley dissolved carbon diox ide in water he tasted the solution and found that he had created a pleasantly tart and refreshing drink, the one we call seltzer or soda water today. The Royal Society awarded him the Copley medal for this. Since it required only flavoring and sugar to produce soda pop, Priestley may be viewed as the father of the mod em soft-drink industry. Priestley’s interest in gases grew. Only three gases were known at the time he began work—air, carbon dioxide, and hydrogen, the last having just been dis covered by Cavendish [307], Priestley changed that drastically for he went on to isolate and study a number of 204 [312] PRIESTLEY PRIESTLEY
them, such as nitrous oxide, in 1772. He collected gases over mercury and thus was able to isolate ones that cannot be collected over water—such as ammonia, sulfur dioxide, and hydrogen chloride, which are water soluble. His experiments earned him membership in the French Academy of Sciences in 1772 and a lu crative post as librarian and companion to Lord Shelburne, who had lost a gov ernment post because of his own liberal tendencies. (He, too, sympathized with the rebellious American colonies.) During his eight years with Lord Shel burne, Priestley did his most interesting work. In 1774, for instance, the mercury he used in his work with gases was the occasion of his most important discov ery. Mercury, when heated in air, will form a brick-red “calx,” which we now call mercuric oxide. Priestley heated some of this calx in a test tube with a lens that he had just obtained and was yearning to use. This concentrated sun light upon the calx. It broke down to mercury again, this appearing as shining globules in the upper portion of the test tube. In addition, a gas was given off that possessed most unusual properties. Com bustibles burned more brilliantly and rapidly in it than in air. Priestley, who accepted the phlogiston theory of Stahl [241], reasoned that the new gas must be particularly poor in phlogiston and there fore accepted the phlogiston of wood so eagerly that the combustion that accom panied phlogiston loss was hastened. Priestley called the new gas “dephlogis- ticated air,” since a couple of years ear lier D. Rutherford [351] had named a gas of opposite properties “phlogisticated air.”
A few years later, Lavoisier [334] killed the phlogiston theory and named the gas oxygen, which is the name it is still known by. Priestley, however, as conservative in chemistry as he was lib eral in politics and religion, remained a convinced phlogistonist to the end of his life.
(Actually Scheele [329] had isolated oxygen a couple of years earlier than Priestley had. Through no fault of Scheele, news of the discovery was not published until after Priestley had re ported on his own experiments. For that reason Priestley is usually given the credit for the discovery.) Priestley experimented enthusiastically with his “dephlogisticated air.” He found that mice were particularly frisky in it and he himself felt “light and easy” when he breathed it. He imagined that breathing “dephlogisticated air” might some day become a fashionable minor vice among the rich. He also recognized the fact that plants restored used-up air to its original freshness by dephlogisticat- ing it. (We say the plants release oxygen into the air.) This observation was sharpened by Priestley’s contemporary, Ingenhousz [306], It is almost anticlimactic to add that Priestley also gave the modern name “rubber” to the product of the South American tree sap which La Condamine [270] had introduced to Europe. He used that name simply because the substance could be used to rub out pencil marks. Priestley’s scientific achievements were not sufficient to make him popular with his neighbors. A Unitarian is not popular among people of more orthodox religion, since Unitarianism denies the divinity of Jesus. Add to that Priestley’s sympa thetic views toward the French revolu tionaries, whose activities were shocking British conservative opinion, and it is not surprising that the populace of Bir mingham (where he had settled in 1780 after retiring on a small pension) viewed him with suspicion. In Birmingham he joined the Lunar Society, which included Watt [316] and Erasmus Darwin [308], who had been its founder. The name of the society was derived from the fact that the meetings were held near the night of the full moon so that members would have something to light their way home. On July 14, 1791, some Birmingham pro-French Jacobins held a celebration in honor of the second anniversary of the fall of the Bastille. An angry mob retal iated against the best-known Jacobin in the city and burned down Priestley’s house. The next Sunday, Priestley took as the text for his sermon, “Father, for give them for they know not what they
[ 3 1 3 ] WOLFF
MESMER [ 3 1 4 ] do.” He managed, eventually, to escape with his family to London. He wasn’t much better off there, for people avoided him as a dangerous radical, particularly after France became a republic, cut off the head of its ex-king, Louis XVI, and went to war with Great Britain. Nor did it help him that the French Republican government made Priestley a French cit izen. (Of course, attitudes toward Priest ley changed after he was safely dead. In 1875, at the centenary of the discovery of oxygen, Birmingham raised a statue to Priestley.) In 1794 Priestley gathered some money and left Great Britain forever just one week before his French colleague Lavoisier was executed by the intolerants of France. Priestley crossed the sea to the land of his old friend Benjamin Franklin, the now independent nation of the United States, where the populace was at that time anti-British and pro French, and where he was welcomed gladly and where he gained the friend ship of Thomas Jefferson [333], The last ten years of his life were spent in peace, and he did much to further the cause of Unitarianism in the new nation. He turned down offers of a Unitarian minis try in New York and of a professorship of chemistry at the University of Penn sylvania. He wanted only a chance to write quietly. [313] WOLFF, Kaspar Friedrich German physiologist Bom: Berlin, January 18, 1734 Died: St. Petersburg (now Lenin grad), Russia, February 22, 1794 In 1759, when Wolff, the son of a tai lor, had just obtained his medical degree from the University of Halle and was serving as army surgeon during the Seven Years’ War, he published a book let on the development of living things that was revolutionary in its implica tions. Until his time many biologists, for example. Bonnet [291], were of the opin ion that a living creature existed pre formed and perfect in every miniature detail in the egg or sperm. Textbooks even had diagrams showing these tiny 2 0 6
"homunculi” within sperm cells, these having been seen, described, and drawn by microscopists with enthusiasm and imagination. Wolff, however, reported that special ized organs arose out of unspecialized tissue. Thus, the tip of a growing plant shoot consists of undifferentiated and generalized cells. As these divide and subdivide, however, specialization de velops and some bits of tissue develop into flowers, while other bits, originally indistinguishable, develop into leaves. Even more important (from our hu man-centered view) was the fact that he could show that this same principle held for a developing animal, such as a chick, within the egg. Undifferentiated tissue gave rise to the different abdominal or gans, he showed, through gradual special ization. Wolff may thus be considered the founder of modern embryology, al though unfortunately his work was largely neglected for over half a century. Nevertheless, it made enough of an im pression on the new Empress Catherine II of Russia (that collector of scholars and lovers) to cause her to invite him to St. Petersburg in 1764, when the Seven Years’ War had ended. He became professor of anatomy and remained there until his death. His name is preserved in several anatomic terms, notably in the Wolffian body, an early form of kidney in embryonic animals preceding the true kidney. [314] MESMER, Franz Anton German physician
den, Germany, May 23, 1734 Died: Meersburg, Germany, March 5, 1815 Mesmer, the son of a forester, entered the University of Vienna in 1759. He began by studying law but shifted to medicine and obtained his medical de gree in 1766. He was a mystic, very much interested in astrology. He was a follower of Para celsus [131] and believed in the existence of cosmic forces permeating the earth
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