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426 [646] HUGGINS
JANSSEN [647] London where he and his wife studied the heavens. After that his interest in as tronomy eclipsed all else. He was one of the first to seize upon the notion of spec troscopy as worked out by Kirchhoff [648] and to grasp to the full its applica tion to astronomy. He studied the spectra of nebulae, of stars, of planets, of comets, and of the sun; of anything, in fact, the light of which he could pass through a telescope and then a prism. In 1863 he announced from a study of spectral lines that the same elements that existed on earth existed in the stars and thus was laid to rest the twenty-one-century-old notion of Aristotle’s [29] that the heavens were composed of a unique substance not found on earth. In 1864 Huggins showed that bright nebulae such as that in Orion consisted of luminous gas, and in 1866 he was the first to study the spectrum of a nova and to show it was enveloped by hydrogen, a gas Angstrom [585] had already detected in the sun. (This was the first indication of a fact that has since been amply confirmed; The universe generally—and the stars in particular—consists mainly of hydrogen.) The spectra of comets had first been studied by Donati [671]. Huggins was able to show that comets are composed at least in part of glowing carbon com pounds. His observations of light reflected from planets, however, yielded no clear conclusions. For these, astrono mers had to await the improved tech niques of the twentieth century. Huggins was also one of the first to experiment with photography as an ad junct of astronomy and by 1875 had devised methods of photographing spec tra. Its importance was that with time exposures, the light from a star or other dim object could be made cumulative and spectra could be developed that had been far too faint to be seen by the naked eye. In addition of course spectra could be recorded permanently by means of photography and measurements upon them conducted at leisure. His most spectacular feat, however, lay in his application of the effect ex pounded two decades earlier by Doppler [534] and Fizeau [620]. Huggins realized that if a star was moving toward the earth, there would be a Doppler-Fizeau shift and all its spectral lines would shift slightly toward the violet end of the spectrum when compared with the posi tion of the lines in the spectrum of a source, such as the sun, that was moving neither toward nor away from the earth. If the star was moving away from the earth the lines would shift slightly to ward the red end of the spectrum. From the amount of shift the velocity of the star in the line of sight could be deter mined. He applied this to the star Sirius in 1868 and found a small “red shift” in one of the hydrogen lines. From this he determined with reasonable accuracy the velocity at which Sirius was moving away from the earth. This motion in the line of sight (radial velocity) is of exceeding importance in astronomy, for it can be determined by shifts in the position of spectral lines, without regard to the distance of the stars. Even the most distant objects in the universe can be (and are) tested for radial velocity as long as their spectra can be obtained. (Proper motion across the line of sight, however, can be ob tained only for the very closest stars.) It was by studying the radial velocity of the vastly distant nebulae that modern no tions of the structure of the universe as a whole have been obtained by men such as Hubble [1136]. Huggins was knighted in 1897 and served as president of the Royal Society from 1900 to 1905. [647] JANSSEN, Pierre Jules César (zhahn-sen') French astronomer
cember 23, 1907 Janssen, the son of a musician, was lame from a childhood accident. He ob tained a degree from the University of Paris in 1852 and then became a travel ing man, in the interests of astronomy. He went to Peru in 1857 to fix the loca 427 [648] KIRCHHOFF KIRCHHOFF
tion of the magnetic equator. He visited Italy, the Azores, and Greece to study solar spectra, volcanoes, and so on. In 1865 he gained a professorial post at the University of Paris. Finally, he met immortality by travel ing to India in 1868 to study the total eclipse. It was then that he observed a strange spectral line and forwarded the data to Lockyer [719], who attributed it to a new element he called helium. Janssen also noted the size of the solar prominences. The day after the eclipse he attempted to take their spectra again and succeeded despite the absence of the obscuring moon. He then announced ju bilantly that it was the day after the eclipse that was the real eclipse day for him.
Lockyer also reported this method of studying prominences without an eclipse. Janssen was the first to note the granu lar appearance of the sun in those areas where it was clear of spots. He traveled to Japan in 1874 to watch a transit of Venus and in 1875 he was official as tronomer on an English expedition to Siam. His most daring voyage of all was by balloon, in 1870, out of the city of Paris, besieged by the Prussians, in order to get to Algeria where he might observe a total eclipse. (Unfortunately, when the time for the eclipse came, the sky was obscured by clouds.) Like Lockyer, he lived to see his ob servation of the helium line vindicated by Ramsay’s [832] discovery of that ele ment on earth. In 1904, toward the end of his life, he published a monumental atlas of the sun, including six thousand photographs of its disc. [648] KIRCHHOFF, Gustav Robert (kirkh'huf) German physicist Born: Königsberg, Prussia (now Kaliningrad, Soviet Union), March 12, 1824
Kirchhoff, the son of a law councillor, studied at the University of Königsberg, graduating in 1847. He was the first to show that the electrical impulse moved at the velocity of light, and he extended and generalized the work of Ohm [461]. His true fame began in 1854 when he was appointed a professor of physics at Heidelberg and began to deliver meticu lous but very dull lectures. There he teamed up with Bunsen [565], with whom he had worked briefly four years earlier at Breslau. Bunsen was interested in pho tochemistry (the chemical reactions that absorb or produce light) and he studied the light produced through colored filters. Kirchhoff, with mathematical in terests and a strong background of New ton [231], suggested the use of a prism. Once this was done the two developed the first spectroscope by allowing the light to pass through a narrow slit before reaching the prism. The different wave lengths of light were refracted differently so that numerous images of the slit were thrown on a scale in different positions and, of course, with different colors. The use of a Bunsen burner, first de veloped by Bunsen in 1857, was helpful. The burner produced so little light of its own that there was no luminous back ground to drown out and confuse the wavelengths of light produced by the re actions studied or by the minerals heated to incandescence. Previous workers, without Bunsen burners, had been misled by the background of luminous lines and bands produced by heated carbon com pounds. Through the use of a spectroscope it quickly became apparent to Kirchhoff that each chemical element, when heated to incandescence, produced its own char acteristic pattern of colored lines. Thus, incandescent sodium vapor produced a double yellow line. In a sense, the ele ments were producing their “finger prints” and the elementary composition of any mineral could be determined by spectroscopy. By 1859 this new analytic method was moving along smoothly and was first publicly reported on October 27 of that year. As was inevitable, a mineral was found displaying spectral lines that had not been recorded for any of the known elements. The conclusion was that a
[648] KIRCHHOFF HITTORF
hitherto unknown element was involved. In this way cesium was discovered, the announcement of the fact being made on May 10, 1860. The name of the element (from the Latin for “sky-blue”) was derived from the color of the most prominent line in its spectrum. Within a year a second element, rubidium, was discovered and that name (from the Latin for “red”) again marked the color of the line that had led to its discovery. This feat was quickly duplicated by Reich [506] and Richter [654] and also by Crookes [695]. Kirchhoff went even further with spec troscopy. He noticed that the bright dou ble line of the sodium spectrum was in just the position of the dark line in the solar spectrum that Fraunhofer [450] had labeled D. He allowed sunlight and sodium light to shine through the same slit in order that the dark line of the first and the bright line of the second might neutralize each other. Instead, the line was darker than ever. From this and other experiments he concluded that when light passed through a gas, those wavelengths were absorbed which that gas would emit when incandescent. This is sometimes called Kirchhoff’s law, although it was discovered by others at about the same time.
If sunlight possessed the D line, then it meant that sunlight passed through so dium vapor on its way to the earth. The only place where the sodium vapor could exist would be in the sun’s own atmo sphere. Consequently, it was possible to say that sodium existed on the sun. In this way he identified half a dozen ele ments in the sun, and others such as Angstrom [585], Donati [671], and Huggins [646] joined in these spectro scopic endeavors. Thus was blasted the categorical statement of the French phi losopher Auguste Comte who, in 1835 had declared the constitution of the stars to be an example of the kind of informa tion science would be eternally incapable of attaining. Comte died (insane) two years too soon to see spectroscopy devel oped.
KirchhofFs banker, unimpressed by this ability to find elements in the sun, asked, “Of what use is gold in the sun if I cannot bring it down to earth?” When Kirchhoff was awarded a medal and a prize in golden sovereigns from Great Britain for his work, he handed it to his banker with the comment, “Here is gold from the sun.” But the gold of the discovery was greater still. Eventually the spectral lines proved to be a guide not only to the great world of the outer cosmos, but to the infra-tiny world within the atom. Balmer [658] made the first steps in this direction. Kirchhoff also pointed out that a per- feet black body—one that absorbed all radiation falling on it, of whatever wave lengths—would, if heated to incan descence, emit all wavelengths. This con clusion had been arrived at indepen dently by Stewart [678]. Although no perfect black body actually existed, one could be constructed by the use of a trick, as Kirchhoff pointed out. A closed container with blackened inner walls and a tiny hole would serve the purpose. Any radiation, of whatever wavelength, that entered the hole would have only an infinitesimal chance of emerging again through the hole and could therefore be considered as ab sorbed. Thus, if the box were heated to incandescence, all wavelengths of light ought to emerge from the hole. The study of this “black-body radia tion” was to prove of the utmost impor tance a generation later, for it was to lead to Planck’s [887] quantum theory. [649] HITTORF, Johann Wilhelm German chemist and physicist Born: Bonn, Rhenish Prussia, March 27, 1824 Died: Münster, Rhenish Prussia, November 28, 1914 Hittorf, the son of a merchant, arrived at physics by way of chemistry and ob tained his doctorate in 1846, having studied under Plücker [521]. In 1852 he was appointed to a professorial position at the University of Münster, a position he held for half a century. Early in his career he worked on 429 [650] WILLIAMSON WILLIAMSON
different forms of selenium and phos phorus. It was easy, however, for a chemist to become interested in the chemical changes that took place when an electric current passed through a solu tion. It was noted, for instance, that the concentration of a dissolved salt in the neighborhood of one electrode grew to be different from that in the neigh borhood of the other as electrolysis pro ceeded. Faraday [474] had explained the passage of electricity through a solution by speaking of ions traveling through the solution under the influence of the cur rent.
Hittorf suggested in 1853 that the ions might travel with unequal speeds so that more would reach one electrode than the other. Thus he evolved the notion of the transport number. This was a valuable concept but nevertheless electrochemistry was not to arrive at maturity until Ar rhenius [894] a generation later was to evolve a comprehensive theory of ioniza tion.
Hittorf also studied cathode rays, to which he had been introduced by Pliicker [521], and in 1869 he antici pated some of the discoveries that Crookes [695] was soon to make in greater detail. Hittorf retired from his position as professor of chemistry and physics at the University of Münster in 1890 because of ill health. [650] WILLIAMSON, Alexander Wil liam English chemist Bom: London, May 1, 1824 Died: Hindhead, Surrey, May 6, 1904
As a child, Williamson (born of Scottish parents) lost an arm and the use of an eye. What counted, however—an intelligent mind—remained. Williamson became interested in chemistry midway through his medical education at Heidelberg, Germany, and, under the influence of Gmelin [457], changed his studies. As a student of chemistry he studied under Graham [547] and eventually worked under Lie big [532], In 1849 he received an ap pointment as professor of chemistry at University College in London. He began a painstaking series of re searches on alcohol and ether and suc ceeded in 1850 in showing the rela tionship between the two. (This was a problem in which Liebig had been greatly interested.) He showed, in effect, that in the alco hol molecule an oxygen atom was at tached to a hydrogen atom and to a hydrocarbon grouping, whereas in ether it was attached to two hydrocarbon groups. He began to classify organic compounds into types according to struc ture. His work helped make clearer the nature and structure of molecules—and this was important, for chemists were in a state of confusion about them. (Final clarification came from Cannizzaro [668] and Kekulé [680] a decade later.) In following the reactions of alcohol and ether Williamson came to under stand how a reaction might go in either direction (a reversible reaction). Thus, two substances might react to form prod ucts that might themselves react to form the original substances again. At some point the two reactions, forward and backward, might match each other in rates so that there would be no overall change in the concentration of reactants and products with time. There would be a dynamic equilibrium, a concept Wil liamson was the first to formulate clearly.
This situation, which Williamson ob served empirically, was to be an impor tant part of the law of mass action, an nounced a decade later by Guldberg [721] and Waage [701] and given com plete theoretical justification on thermo dynamic grounds by Gibbs [740] two decades later. Williamson suggested in 1854 that the reason sulfuric acid was needed in the formation of ether from alcohol was that first there was a combination of alcohol and sulfuric acid to form ethyl sulfate. The ethyl sulfate thus produced reacted with additional alcohol to form ether, liberating sulfuric acid in the process. The sulfuric acid, first joining the alco hol then being released again, was un changed and unconsumed at the end of
[651] HOFMEISTER KELVIN
the reaction, yet was necessary to it, and thus acted as a catalyst. For the first time, catalytic action was clearly ex plained by means of the formation of an intermediate compound. Later, such men as Michaelis [1033] showed how this concept was essential to the explanation of enzyme action. Williamson was the first to produce a mixed ether—one in which the oxygen atom is attached to two different hydro carbon groupings. The chemical reaction he used for the purpose is still called the Williamson synthesis. [651] HOFMEISTER, Wilhelm Frie drich Benedikt (hofe'my-ster) German botanist Born: Leipzig, Saxony, May 18, 1824
Died: Leipzig, January 12, 1877 Hofmeister was the son of a music publisher who was an accomplished bot anist in his off hours. Hofmeister himself eventually ran the business and was a botanist, too, even more seriously and successfully than his father had been. Hofmeister did not receive an aca demic education at all, but his work earned him a sufficient reputation to get him a professorial appointment at Hei delberg in 1863. He was extremely nearsighted and would not wear glasses, so that he was forced to peer very closely at his work. This apparently encouraged him to de vote himself to delicate manipulation and microscopic work. Thus, in 1847 he was able to describe in detail the manner in which the plant ovule developed into an embryo. He also examined the pro cess of cell division and showed that the nucleus did not truly disappear in the process. He seems to have been almost on the point of discovering chromosomes and anticipating Flemming [762], He studied simple plants and was the first to show “alternation of generations” in mosses and ferns, a sexually-reproduc ing form alternating with an asexually- reproducing one. He also showed the relationship of the gymnosperms (the cone-bearing trees, such as pines) to the other broad groups of plants. Hofmeister is considered the father of modern botany, but in later life he be came intolerant of criticism and, like Berzelius [425], very stubborn in persist ing in his errors. His rage at criticism and his attempt to be both a busi nessman and a botanist each contributed to his early death. [652] KELVIN, William Thomson, Baron
Scottish mathematician and physi cist
Born: Belfast, Ireland, June 26, 1824
Died: near Largs, Ayr, December 17, 1907 Lord Kelvin was born William Thom son. He was the son of an eminent math ematician and was an infant prodigy who attended his father’s lectures with delight when only eight years old. At eleven he entered the University of Glas gow, where he finished second in his class in mathematics. His first paper on mathematics was written while he was still in his teens, and was read to the Royal Society of Edinburgh by a profes sor well along in years, since it seemed undignified for the staid assemblage to be lectured to by a schoolboy. In 1841 he went to Cambridge. After graduation, in 1845, Thomson traveled to Paris for postgraduate work and studied under Regnault [561]. Both father and son were in their time professors at the university, the father in mathematics, the son in natural philoso phy (the old-fashioned name for sci ence). The younger Thomson held his chair for over half a century. He was one of the first to teach physics in the laboratory (converting an old wine cellar in a professor’s house into one for the purpose) as well as the lecture hall. He lectured most dramatically, by the way, even eccentrically. In 1846, the same year in which he obtained his professorial position, Thom son announced his calculation of the age of the earth from basic physical princi- Download 17.33 Mb. Do'stlaringiz bilan baham: 
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