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- [477] MURCHISON
316 [474] FARADAY
FARADAY [474] make one faraday. (Also, the unit of electrostatic capacitance is the farad, in his honor.) Faraday, like almost every contem porary scientist, was struck by the exper iment of Oersted [417] showing that an electric current is capable of deflecting a magnetic needle. In 1821, the year after this announcement, Faraday constructed a device consisting of two vessels of mer cury, each attached to a battery by a metal rod entering the mercury liquid from the bottom of each vessel. The upper levels of the mercury were bridged by a curved metal bar dipping into the mercury in both containers. Thus there was a completed circuit. One end of the curved bridge was fixed in the container, while to the lower rod a small movable magnet was attached—one that could ro tate about the fixed upper rod. In the other container a fixed magnet extended upward into the mercury from the lower rod, while the bridge on that side ended in a hinged wire that dipped into the mercury and was free to rotate about the fixed magnet. When Faraday turned on the current the movable wire began to pivot about the fixed magnet, while the movable magnet pivoted about the fixed wire. In this way Faraday successfully converted electrical and magnetic forces into con tinual mechanical movement. (It was at this point, it would seem, that Davy’s jealousy of Faraday broke into the open. He implied that Faraday had got his idea for the experiment from a conversation between himself and Wol laston that Faraday had overheard. Faraday protested that the conversation may have turned his attention in the di rection of electrical experimentation but that his device was nothing like the one discussed. And, to be sure, experiments that Davy and Wollaston had conducted had failed. Moreover, Wollaston had ex pected the wire to rotate on an axis rather than to revolve about another wire. These days it is accepted that Fara day was correct and that his work was independent. Unlike Davy, Wollaston ex hibited no resentment at all but was al ways friendly to Faraday.) Although Faraday’s whirling wires and magnets were interesting and novel, his simple electric motor was only a scientific toy, on a level with Hero’s [60] steam engine. He was after much bigger game. Since Oersted had produced mag netic attraction out of an electric cur rent, Faraday wanted to reverse matters and produce an electric current out of magnetic attraction. To bring this about, he wound a coil of wire around one segment of an iron ring. This coil was attached to a battery. The circuit could be opened or closed by a key. If he closed the circuit a magnetic field would be set up in the coil as Ampère [407] had shown and it would be concentrated in the iron ring as Stur geon [436] had shown. Suppose, then, that a second coil is wrapped around another segment of the iron ring and connected to a gal vanometer. The magnetic field created in the iron ring by the first coil might set up (by reverse action) a current in the second coil, and the galvanometer would indicate that induced current. The experiment worked and Faraday had invented the first transformer, but it did not work in the manner Faraday had expected. There was no steady flow of electricity in the second coil to match the steady magnetic force set up in the iron ring. Instead, there was a momen tary flash of current, marked by a jerk of the galvanometer’s needle when he closed the circuit; and a second flash, in the opposite direction, when he broke the circuit. (Ten years before, Ampère had observed the same fact, but it did not fit his theories and he dismissed it.) To Faraday, this observation required explanation. Because Faraday was un educated, he was completely innocent of mathematics (perhaps the greatest scien tist in history of whom this was true). He made up for this through his intuitive ability to pictorialize, an ability perhaps unequaled in scientific history. He had dropped iron filings on a paper under which a magnet was located and noticed the regular patterns they took up when the paper was tapped. (So had Peter Peregrinus [104] six centuries be fore.) Faraday was also aware of Am 317 V [474] FARADAY
FARADAY [474] pere’s demonstration that a magnetic force circled a wire carrying a current. He began to visualize the magnetic force, then, as stretching out in all direc tions from the electric current that served as its starting point. It filled space as a kind of magnetic field. Lines could be drawn through that field representing all points where the strength of the mag netic force was equal. These Faraday called lines of force, and it was along these lines, it seemed to him, that the iron filings aligned themselves, thus mak ing them “visible.” It was possible to work out the form of the lines of force for wires, for bar magnets, for horseshoe magnets, even for globular magnets such as the earth. This was the beginning of a picture of the universe as consisting of fields of various types, one that was more subtle, flexible, and useful than the purely mechanical picture of Galileo [166] and Newton [231], The field uni verse was to be recognized with Maxwell [692] a half century later and with Ein stein [1064], after an interval of another half century. Faraday’s pictorial and nonmathemat ical imagination visualized these lines of force as real fines. When a circuit was closed and electricity was set to flowing, the lines sprang outward into space. When the circuit was broken they col lapsed inward again. Faraday decided then that an electric current was induced in a wire only when lines of force cut across it. In his transformer, when the current started in the first coil of wire, the expanding lines of force cut across the wire of the second coil and ac counted for the short burst of electric current. Once the original current was established, the lines of force no longer moved and there was no current in the second coil. When the circuit was bro ken, the collapsing fines of force cut across the second coil in the opposite di rection and a burst of electric current resulted again, but in the direction oppo site to that of the first. Faraday, at the time, was giving enor mously popular lectures in science for the general public, quite after the fash ion of his old master, Davy. Indeed, after the popular Davy had resigned, the 318 Royal Institution nearly went bankrupt, as before Davy’s time. It was only with Faraday’s lectures that the Institution recovered. Faraday’s new career began when he was forced to give an impromptu lecture after a regularly scheduled lecturer, Wheatstone [526], was unable to appear. Faraday proved so excellent a lecturer that the novelist Charles Dickens, no mean lecturer himself, was among Fara day’s admirers, while Prince Albert, the husband of Queen Victoria, and Prince Edward, her son (and later Edward VII), attended them too. Faraday always included special Christmas lectures for youngsters on his schedule and one of these, The Chemical History of a Can
able classic. (It was the first complete book to be converted into “basic En glish.”)
In any case, it was during one of these lectures that Faraday demonstrated the theory involving the lines of force both to himself and to the audiences by insert ing a magnet into a coil of wire attached to a galvanometer. While the magnet was being inserted or removed, current flowed through the wire. If the magnet was held stationary and the coil moved over it one way or the other, there was current in the wire. In either case the magnetic lines of force about the magnet were cut by the wire. If the magnet and coil were both held motionless, whether the magnet was within the coil or not, there was no current. Faraday had thus discovered electrical induction, a discovery made indepen dently and at about the same time by the American physicist Henry [503]. It was to lead to great things, but this was not at once apparent. Faraday was an inspiring teacher who caught the interest of men such as Dan- iell [470] and Perkin [734]. His theory of the fines of force (which he published in 1844) was not taken too seriously at first. However, when Maxwell came to tackle the matter of electromagnetism with precise mathematical tools, he was to end with the same picture, mathe matically phrased, that Faraday had drawn in simple words.
[474] FARADAY
FARADAY [474] Once Faraday had demonstrated that electricity could be induced by magne tism, the next step was to do so con tinuously and not in short spurts. He ac complished this by adapting in reverse an experiment first described by Arago [446], Arago had shown that a rotating copper wheel could deflect a magnet sus pended over it because (Faraday now saw) the wheel was cutting through the magnetic lines of force so that electric currents were being set up in it, these in turn setting up a magnetic field that deflected the magnet. But Faraday did not want an electric current setting up a magnetic field; he wanted a magnetic field setting up an electric current. Faraday therefore turned a copper wheel in such a fashion that its edge passed between the poles of a permanent magnet. An electric current was set up in the copper disc then, and it continued to flow as long as the wheel continued to turn. That current could be led off and put to work and Faraday had invented the first electric generator. This was ac complished in 1831 and was probably the greatest single electrical discovery in history.
It was only necessary to set a steam engine or water power to turning the copper disc and the energy of burning fuel or of falling water could be con verted into electricity. Until Faraday’s time the only source of electric current was the chemical battery, which was ex pensive and small-scale. Now there was for the first time the possibility of a large and cheap supply of electric current. It took a half century and more for subsid iary inventions to make this entirely practical and the generators that eventu ally did the work look nothing at all like Faraday’s turning wheel. But the line of descent is clear and the results of the final development we all know. In later years Faraday made more dis coveries in connection with electromag netism and its interaction with light. In 1839, however, he suffered a men tal breakdown and, like Newton, he was never quite the same again. Failing memory drove him out of the laboratory (he refused to work when he could no longer trust himself to work capably, nor would he use an assistant) and saddened his last years. It is possible that this is another case, like those of Scheele [329] and Davy, of a chemist suffering from chronic, low-grade poisoning. Faraday was an extremely religious man who, after his marriage in 1821, joined his wife’s church, the splinter sect of Sandemanians, a sect that no longer exists. This sect eschewed worldly vanity, and Faraday accepted the dozens and dozens of honors, medals, degrees, and miscellaneous embroidery with polite distaste. When Lord Melbourne offered him a pension in what seemed an offen sively patronizing fashion, Faraday quietly left and would not return until Melbourne apologized. It was not his own honor for which Faraday was con cerned (he explained) but that of sci ence. The only honor he valued was mem bership in the Royal Society, to which he had been elected in 1824 against Davy’s embittered opposition. Davy, in fact, cast the only negative vote. Faraday strongly favored a more im portant role for science in education, but he could not bring his gentle soul into al liance with the more radical Babbage [481] in the latter’s violent attacks on the Royal Society and on Great Britain’s scientific policy generally. When, in 1857, Faraday was eventu ally offered the presidency of the Society by Tyndall [626], he declined, and he also declined an offer of knighthood. He was intent on being plain Michael Fara day and on loving only science. He turned down chances for more money even when the duke of Wellington him self suggested he engage in more prac tical—and profitable—labors. In 1844 Faraday was invited to dinner with Queen Victoria on a Sunday, when he was due at the small church he at tended. After an agonizing period of un certainty he decided it was necessary for him to obey the queen, but the inflexible congregation excommunicated him and he could not be reinstated until he had undergone considerable penance. His religious beliefs enabled him, how ever, to solve without fear or uncertainty a problem that agonizes many scientists
[475] ENCKE
MURCHISON [477] of our day—the conflict between the demands of country and of human ide alism. During the Crimean War of the 1850s (in which Great Britain was at war with Russia) Faraday was asked by the British government if there was any possibility of preparing quantities of poi son gas for use on the battlefield and if he would head a project to perform the task, supposing it to be feasible. Faraday answered at once and with finality that the project was certainly feasible, but that he himself would have absolutely nothing to do with it. He kept a meticulous day-by-day rec ord of his forty-two years of scientific la bors (1820-62). This was published in 1932 in seven volumes. Faraday began to lose his ability to think clearly after 1855, perhaps because (some think) of chronic mercury poison ing. He retired, uncomplainingly, from his work and waited patiently for death. He requested during life that he be buried under “a gravestone of the most ordinary kind” and that only a few rela tives and friends attend his funeral, and this was done. His true memorial, of course, is our electrified world of today. [475] ENCKE, Johann Franz (enk'uh) German astronomer Born: Hamburg, September 23, 1791
Died: Spandau (near Berlin), August 26, 1865 Encke, the son of a minister, entered Gottingen in 1811 and studied under Gauss [415], then served as an artillery officer at the tail end of the Napoleonic Wars. Back in civilian life he took up astron omy and in 1819 computed the orbit of a comet that had been observed the year before by Pons [376], The comet proved to have a period of only three and a third years. Encke’s comet, as it has been called ever since, was the second comet whose return was predicted, the first being Halley’s [238], Encke’s comet was the first short-period comet to be discov ered, and no comet has ever been found with a shorter period. In 1835 Encke’s comet passed close enough to Mercury to allow the mass of that planet to be determined for the first time—from the effect of its gravity upon the comet’s orbit.
In later life Encke calculated the dis tance of the sun (from data on past transits of Venus) to be 95,300,000 miles. This is over 2 percent too high a figure, but it was the most accurate value obtained at that time. In 1825 Encke was made director of the Berlin Observatory, which in ten years he transferred to a larger, magnificently equipped building. [476] PETIT, Alexis Thérèse (puh-teeO French physicist Born: Vesoul, Haute-Saône, Oc tober 2, 1791 Died: Paris, June 21, 1820 Petit obtained his doctorate in 1811, then taught at École Polytechnique. Al though he did much work on heat, Petit is remembered almost exclusively for the work he did with Dulong [441] and for the law of Dulong and Petit. He was also the brother-in-law of Arago [446]. He was another of the scientists of the period to be victimized by that killer of young adults, tuberculosis.
(muriki-son) Scottish geologist
ruary 19, 1792 Died: London, October 22, 1871 Murchison, the descendant of a land owning family, was left fatherless at four. He had a military education and took part in the campaign in Spain against the forces of Napoleon. After ward, as befitted a retired officer, he be came a renowned fox hunter. He was lured by Davy [421] into attending scientific lectures, became enamored of geology and sold his hunting dogs. He began as a neptunist but was soon con verted to vulcanism. He explored Great Britain and then with Lyell [502] and Sedgwick [442] ex tended his curiosity to the rocky features 320 [478] BAER
BAER [478] of much of western Europe. He studied the rocks of what he called the Silurian era (named for an old Celtic tribe in Wales that had lived in the area where Murchison found the rocks) and for this received the Copley medal of the Royal Society. With Sedgwick he next studied rocks of the Devonian era (from Devon, in southwest England). In the 1840s he headed a geologic sur vey to the Ural Mountains in Russia. This resulted in the naming of the Perm ian era, from the city of Perm in the Urals. In 1846 he was knighted. [478] BAER, Karl Ernst von (bare) German-Russian embryologist
1792
Died: Dorpat, Estonia (now Tartu, Estonian SSR), November 28, 1876 As was usually the case with nine teenth-century Russians, the need for higher education made a trip to Ger many necessary. This was easier for Baer since he was of German descent, as were most of the landowners in the Baltic provinces of Russia in those days. He obtained a medical degree at Dorpat in 1814, but then obtained further training in Berlin and Vienna. After achieving that education he eventually returned to Russia. His greatest discoveries, how ever, took place in Germany, where he served as a professor at the University of Königsberg from 1817 to 1834. In 1827 he published his findings in connection with the mammalian egg. The mammalian ovary contains certain structures called follicles, which had been discovered by Graaf [228] a cen tury and a half before. Since that time the follicle had been taken to be the mammalian egg. Baer opened the follicle of a dog and examined a small yellow point within. It was this much smaller structure, seen only in a microscope, that was the mammalian egg—and so it was finally clear that mammalian develop ment (including human development, of course) was not fundamentally different from that of other animals. Between 1828 and 1837 he published a two-volume textbook on embryology, which may be considered, along with the work of Pander [489], as founding the subject. Building on Pander’s observa tions, Baer pointed out that the develop ing egg forms several layers of tissue, each of which is undifferentiated but out of which various specialized organs de velop, a given set of organs from a given layer. These he called germ layers— germ being a general term for any small object that contains the seed of life. (Nowadays there is too great a tendency to think that by germ is meant only bac terium.) Baer thought there were four such germ layers, but later Remak [591] pointed out that the two middle layers really form a single structure, so that a total of three layers exist, and that has remained the view ever since. In his doctrine of germ layers, Baer was taking up the cause of epigenesis, which had first been enunciated by Wolff [313] three quarters of a century before. With Baer the victory of that doctrine was complete. Baer’s studies of embryos also supplied new ammunition for those biologists who believed in the evolutionary development of life. Baer pointed out that the early stages of the development of vertebrate embryos were quite similar even among creatures that in the end were quite dis similar. Small structures in different em bryos, scarcely distinguishable from each other at first, might develop into a wing in one case, an arm in another, a paw in a third and a flipper in still a fourth. Baer believed that relationships among animals could be deduced more properly by comparing embryos than by compar ing adult structure (so that he is also the founder of comparative embryology). Baer pointed this up dramatically when he was able to show that the early vertebrate embryo possessed a notochord for a short while. The notochord is a stiff rod running the length of the back, and there are very primitive fishlike creatures that possess such a structure throughout life. In vertebrates this is quickly re placed by a spinal cord, but the tempo rary existence of the notochord in the vertebrate embryos shows their rela
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