Biographical encyclopedia
Download 17.33 Mb. Pdf ko'rish
|
|
331 [497] CARNOT
RETZIUS [498] His brother’s son was eventually to serve as one of the presidents of France’s Third Republic. Among this group of politicians was Nicolas, a scientist. He was educated by his father to begin with, entered the École Polytechnique in 1812 and gradu ated in 1814. He had been trained as a military engineer and fought against the armies invading France in 1814. With Napoleon’s fall his father was exiled and his own advancement was out of the question. He remained an army officer, however. In 1824 he published his only work, a partial title of which is On the Motive
secure his place in the history of science. In it he defined work as “weight lifted through a height.” (This is now made more general by defining it as “force act ing through a distance against resis tance,” a definition advanced by Coriolis [480].)
Carnot was interested in the amount of work that could be obtained from a heat engine. The steam engine invented by Watt [316], although far better than any previous model, was quite inef ficient. In Carnot’s time an efficiency of 5 to 7 percent was all that could be expected, meaning that 93 to 95 percent of the heat energy of the burning fuel was wasted. Carnot was interested in de termining how far this mark might be improved. He was able to demonstrate that the maximum efficiency depended upon the temperature difference in the engine. In the case of the ordinary steam engine, the temperature of the steam (T, ) was the hottest part of the engine, the tem perature of the cooling water (T2) the coldest. The maximum fraction of the heat energy that could be converted into work, even if the machine operated with perfect efficiency, would then be:
~
T 2 t 2 (Ti and T2 in this equation represent absolute temperature, a concept that was to be made clear and explicit by Kelvin [652] some fifteen years after Carnot’s death. Indeed it was Kelvin who brought Carnot’s till-then-neglected work to the attention of science in 1848.) Carnot was the first to consider quan titatively the manner in which heat and work are interconverted. He was thus the founder of the science of thermo dynamics (“heat movement”). He was not correct in his views as to the nature of heat flow, for he held to the caloric theory of Lavoisier [334]. This, however, did not affect the validity of his results. Carnot’s equation makes it clear that what counts in maximum work produc tion are the maximum and minimum temperatures. It does not matter what happens to the temperature in between, whether it drops slowly, quickly, smoothly, or in stages. The dependence on two extreme points only and indepen dence of the path between is charac teristic of thermodynamic function. G. H. Hess [528] a decade later showed this to be true about the heat accom panying chemical reactions. It is possible from Carnot’s equation to deduce what is now called the second law of thermodynamics and Carnot was the first to be vouchsafed a glimpse of that great generalization. He might well have gone on to bring it into the full light of day. Unfortunately, he died in a cholera epidemic at the age of thirty-six and his work was neglected. It was left to such men as Clapeyron [507] and Clausius [633], a generation later, to develop Carnot’s notions. [498] RETZIUS, Anders Adolf (ret'- see-us)
Swedish anatomist Born: Stockholm, October 13, 1796
Died: Stockholm, April 18, 1860 Retzius, the son of a professor of nat ural history, studied at the University of Copenhagen under Oersted [417] among others. He obtained a medical degree in 1819 from the University of Lund and in 1824 was appointed professor of anat omy at the Caroline Institute in Stock holm. His most important contribution was in anthropology. Mankind has always been aware of differences between 332 [499] BEER
MOSANDER [501] groups of human beings—skin color, for instance. In 1842 Retzius attempted to impose an objective and measurable cri terion by using the skull. The ratio of skull width to skull length, multiplied by 100, he called the cranial index. A cra nial index of less than 80 was dolichoce phalic (“long head”); one of over 80 was brachycephalic (“wide head”). In this way Europeans could be divided into Nordics (tall and dolichocephalic), Med iterraneans (short and dolichocephalic), and Alpines (short and brachycephalic). This was not a satisfactory criterion of race, but it set the stage for other at tempts to deal objectively with this ex traordinarily difficult subject, attempts that only today through the careful anal ysis of blood groups are beginning to yield results. The evils of racism—such as slavery in America and the infamies of Nazi Germany—were given a pseudo scientific justification by men who made use of anthropological terms like those of Retzius to serve their own purposes. [499] BEER, Wilhelm (bayr) German astronomer Born: Berlin, January 4, 1797 Died: Berlin, March 27, 1850 Beer was a banker by profession and came of a Jewish family. One of his brothers was a composer who wrote under the name of Giacomo Meyerbeer. Beer’s hobby was astronomy. He built an observatory and, with the help of Madler [488], spent eight years locating the prin cipal features of the moon with great ac curacy and measuring the heights of a thousand mountains after the fashion of Galileo [166]. The final map, published in 1836, and based on six hundred nights of careful observation, showed the moon a meter in diameter and was a far cry from Ric- cioli’s [185] map of two centuries before. Through all the eight years, no change was observed in any lunar feature, dra matic evidence that the moon was, at least for the most part, a dead and static world. In his discussion of the map, Beer speculated on the usefulness of an as tronomic observatory on the moon which now—a century and a quarter later—ap pears on the horizon of the possible. In 1830 Beer proceeded to the map ping of the planet Mars and was the first to make a definite picture of lighter and darker areas. On his map there was no sign of the canals that, thanks to Schia parelli [714], were to make such a stir a half century later. [500] POISEUILLE, Jean Léonard Marie (pwah-zoy'yuh) French physician Bom: Paris, April 22, 1797 Died: Paris, December 26, 1869 Poiseuille, the son of a carpenter, stud ied at the École Polytechnique and gained his doctor’s degree in 1828. He was particularly interested in blood circulation and improved on Hales’s [249] method of measuring blood pres sure by using a mercury manometer for the purpose, instead of allowing the blood to rise in a long tube. In order to study the manner in which blood made its way through the fine capillaries, Poiseuille studied flow of water in such tubes. He found that the rate of flow depended on diameter and length of the tubes and the pressure difference between the two ends. He worked out an equation, including these values and the temperature, and this was eventually termed Poiseuille’s law. Flow depends on the viscosity of the liquid, too, and the unit of viscosity is the poise, named for Poiseuille. [501] MOSANDER, Carl Gustav (moh- sawn'der) Swedish chemist Born: Kalmar, September 10,1797 Died: Angsholm, October 15, 1858 Mosander was first apprenticed to an apothecary, went on to study medicine, and obtained his medical degree in 1825. He served as an army surgeon for some years. His lifework began as assistant to Berzelius [425], in whose house he lived for a long time and to whose teaching duties he succeeded when Berzelius re
[502] LYELL
LYELL [502] tired in 1832. Mosander held the post till his death. As was natural for a Swedish chemist, he interested himself in the rare earth minerals discovered in Sweden by Gado- lin [373]. It was Mosander more than anyone else who revealed the complexity of the rare earths. In 1839 he studied a compound of cerium, an element already discovered in those minerals by Berzelius and others, including Klaproth [335]. In the com pound he discovered a new element, which he named lanthanum from a Greek word meaning “hidden” because it had been hidden so effectively in the minerals. He did not publish at once but, sus pecting that he was not through, contin ued his investigations. In the early 1840s he isolated four other rare earth ele ments, yttrium, erbium, terbium, and di dymium. The first three were named after Ytterby, the quarry in which the minerals were first located, and the last from the Greek word for “twin” because it was so like lanthanum. (In the end, didymium proved to be a mixture of two elements, which were not separated until Auer [890] turned the trick four decades later.)
By the time Mosander was done there was no question but that there was a whole series of very similar rare earth el ements. These were to remain a puzzle to chemists for three quarters of a cen tury until Bohr [1101] and others worked out the electronic structure of the atom well enough to account for the properties of the rare earth elements. [502] LYELL, Sir Charles Scottish geologist
Angus), November 14, 1797 Died: London, February 22, 1875
At Oxford, from which he graduated in 1819, Lyell, the son of well-to-do par ents, went on to study law and, in 1827, was finally accepted for the bar. Lectures on geology fascinated him, however, and he gave more and more of his time to the subject. His Oxford teacher had been a neptunist after the fashion of Werner [355], but Lyell’s own investigations dur ing trips to the Continent inclined him more and more to vulcanism and to the principle of uniformitarianism that, un known to him, Hutton [297] had ex pounded a generation earlier. In a trip to Paris in 1833, he was further stimulated by meeting Cuvier [396] and Humboldt [397]. He also read Lamarck’s [336] book and was impressed. When he finally encountered Hutton’s book, he recognized that it paralleled his own views. Furthermore his travels in France and Italy made it possible for him to bring together a large collection of data as confirmation of Hutton’s view that the slow processes of heat and ero sion (still proceeding today) had gradu ally brought about all the changes on earth without the necessity of supposing any catastrophes. Indeed, Lyell was, if anything, too extreme in his uniformi tarianism and was unready even to admit the possibility of mild and limited catas trophes. (Nowadays geologists believe that something drastic occurred at the end of the Cretaceous, something that killed off the dinosaurs—something as dramatic perhaps as the strike of an as teroid that nearly sterilized the earth.) Lyell did not contribute anything fun damentally new to geology, though it was he, applying the suggestions of the classical scholar William Whewell [487], who first named a number of the geo logic eras, such as the Eocene, Miocene, and Pliocene. He also estimated the age of some of the oldest fossil-bearing rocks at the then-unheard-of figure of 240,000,000 years—but that is still less than half the currently accepted figure. His most important deed was to popu larize and amplify the Huttonian view in a book called The Principles of Geology, which appeared in three volumes be tween 1830 and 1833 and went through twelve editions in his lifetime. In 1834 he received a medal from the Royal So ciety for his work. Some of Lyell’s conservative col leagues refused at first to accept his theories, since they seemed to lead inevi tably to some form of evolutionary doc trine. That, after all, was the bugaboo of 334 [503] HENRY
HENRY [503] the time for conservative scientists, as Copernicanism had been the bugaboo two and a half centuries before. And in deed the conservatives were right to fear it, for among the scholars who accepted Lyell quite early was the young Charles Darwin [554]. Lyell’s book, clearly and attractively written, sold well. Noted geologists like Murchison [477] and Sedgwick [442] began to study the crust of the earth along Huttonian lines. The principle of uniformitarianism became popular, par ticularly in England, and in the 1840s Lyell visited the United States and lec tured to enthusiastic crowds. Before long the catastrophism of Cuvier [396] was dead, though it maintained itself in France into the 1850s. Lyell formed a close friendship with Darwin (who was himself something of a geologist in his younger days) and when Darwin’s great book on evolution came out, Lyell was one of the first con verts to his friend’s views. In fact, Lyell carried Darwin’s evolu tionary views into the most sensitive field of all, that involving the development of man, and this at a time when even Dar win himself was not prepared to do so. In 1863 Lyell wrote The Antiquity of Man, basing his evidence for man’s an tiquity on old artifacts of the type that had been uncovered by Boucher de Perthes [458], As another example of his unconventionality, Lyell was one of the strong proponents of the North during the American Civil War, when the En glish “better classes” were largely pro- Southem. Lyell was knighted in 1848 and created a baronet in 1864. He died while working on the 12th edition of his great book. Despite his unsettling views with regard to the evolution of earth and man, he was buried in Westminster Abbey in appreciation of his services to science. [503] HENRY, Joseph American physicist
cember 17, 1797 Died: Washington, D.C., May 13, 1878
The life of Joseph Henry paralleled that of Faraday [474] in many ways. Henry, like Faraday, came of a poor family. He was the son of a day laborer, had little schooling, and was forced to go to work while young. Faraday was ap prenticed to a bookbinder, and Henry, at thirteen, was apprenticed to a watch maker. Henry was the less fortunate, since he didn’t have Faraday’s associa tion with books. At least he might not have had, except for an odd happening. The story goes that at sixteen while Henry was on vacation at a relative’s farm, he chased a rabbit under a church building. He crawled underneath, found some of the floorboards missing and promptly abandoned the rabbit to ex plore the church. There he found a shelf of books. One was a book called Lec tures on Experimental Philosophy, which he began leafing through. Before that, he had been playing with the notion of becoming a writer, but now he was fired with curiosity and a new ambition. The owner of the book let the young man keep it and Henry returned to school. He entered the Albany Academy, teaching at country schools and tutoring privately on the side to earn his tuition, and eventually graduated. He was set to study medicine when an offer of a job as surveyor turned him toward engineering. By 1826 he was teaching mathematics and science at Albany Academy. Like Faraday he grew interested in the experiment of Oersted [417], and he be came the first American to experiment with electricity in any important way since Franklin’s [272] pioneer work three quarters of a century earlier. Sturgeon [436] had put Oersted’s work to use in the form of an electromagnet. In 1829 Henry heard of this in the course of a visit to New York and thought he could do better. The more coils of conducting wire one could wrap around an iron core, the greater the rein forcement of the magnetic field and the stronger the magnet. The only trouble was that when one started to wrap more and more wires about the coil, they touched and short-circuited. It was necessary, therefore, to insulate the wires. Insulation would not interfere
[503] HENRY
HENRY [503] with the magnetic field setup, but it would prevent short-circuiting. Insulation was not easy to come by in those pre electrical days, so Henry tore up one of his wife’s silk petticoats for the purpose (a sacrifice to science she could scarcely have been overjoyed with). In the years to come a great deal of Henry’s time was put into the brutally boring task of slowly wrapping insulation about wire. The electromagnet he made was far more powerful than Sturgeon’s. He made others, more powerful still, and by 1831 had developed one that could lift 750 pounds as compared with the 9 pounds that was the best Sturgeon could ever do. The same year, in a demonstration at Yale University, another of his elec tromagnets, using the current from an ordinary battery, lifted more than a ton of iron. In 1832 he reaped his reward in the form of a professorial appointment at Princeton. But electromagnets were more than a matter of brute strength. Henry built small, delicate ones that could be used for fine control. Imagine a small elec tromagnet at one end of a mile of wire, with a battery at the other end. Suppose you could send a current through the wire by pressing a key and closing the circuit. With the current flowing, the electromagnet, a mile away, could be made to attract a small iron bar. If the key were then released, the current would be broken, the electromagnet would lose its force, and the small iron bar would be pulled away by a spring at tached to it. By opening and closing the key in a particular pattern, the iron bar a mile away could be made to open and close, clicking away in that same particu lar pattern. By 1831 Henry was doing just this. However, the longer the wire, the greater its resistance and, by Ohm’s [461] law, the smaller the current flowing through it. There is a practical limit, then, to the distance over which such a pattern can be sent. To circum vent that, Henry invented the electrical relay in 1835. A current just strong enough to activate an electromagnet would lift a small iron key. This key when lifted would close a second circuit with a current (from a nearby battery) flowing through it. This in turn could ac tivate another relay. In this way the cur rent would travel from relay to relay and could cover huge distances without weak ening. The opening and closing of a key could then impress its peculiar pat tern through any distance. In effect Henry had invented the tele graph. However, he did not patent any of his devices for he believed that the discoveries of science were for the benefit of all humanity. As a result, it was Morse [473] who worked out the first telegraph put to practical use (in 1844) and it is Morse who usually gets credit as the inventor. In tackling the technical end of the problem, Morse, who was completely ignorant of science, was helped freely by Henry. In England, Wheatstone [526], after a long confer ence with Henry, worked up a telegraph in 1837. Henry, an idealist, did not mind not sharing in the financial rewards of the telegraph. It bothered him, however, that neither man ever publicly acknowl edged Henry’s help. Henry missed the credit for a more important discovery and did so in a more heartbreaking way. At the Albany Academy, Henry’s teaching duties were so heavy that he could turn to research only in the vacation month of August. In August of 1830 he discovered the princi ple of induction; that is, how an electric current in one coil may set up a current in the other through the development of the magnetic field. He had not quite finished his work at the end of the month so he put it aside for the next Au gust. Well before the next August he read Faraday’s preliminary note concerning his discovery of induction. Henry rushed back to his experiments and published his own work, but by then it was too late. Henry had done the key experi ments ahead of Faraday, but Faraday had published first. Henry was not one to feel bitter and always freely admitted Faraday’s priority. In Henry’s paper, however, he ex plained that the electric current in a coil can induce another current not only in another coil but in itself. The actual cur
Download 17.33 Mb. Do'stlaringiz bilan baham: 
|