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661 [1049] BARKLA
BEEBE [1050] own experiments, maintained that it was the addition of oxygen that was crucial and that this addition was catalyzed by enzymes containing iron atoms. As it turned out this was a particularly fruitful controversy, for both parties were right. Together they made a good start toward working out the respiratory chain in tissues, the route by which the body slowly converted organic molecule to water and carbon dioxide, producing available energy in the process. Meanwhile, the steroids, of which cho lesterol and the bile acids were examples, grew to seem of greater and greater im portance to life. At least one of the vita mins, vitamin D, was closely related to steroids and, among the hormones, those controlling sexual development and re production were steroids. As a result, Wieland, who was recognized as one of the chief elucidators of the steroid struc ture, was awarded the 1927 Nobel Prize in chemistry. During World War II, Wieland was openly anti-Nazi and some of his stu dents were involved in the 1944 treason trials. Wieland survived the war and Nazism, however, by a dozen years. [1049] BARKLA, Charles Glover English physicist Born: Widnes, Lancashire, June 27, 1877 Died: Edinburgh, Scotland, Octo ber 23, 1944 Barkla studied at University College, Liverpool, where one of his teachers was Oliver Lodge [820], While still a student Barkla substituted for Lodge as lecturer when necessary. After graduation Barkla spent time at Cambridge under Thomson [869] (where he was also a prominent member of a choral group, singing bari tone), returning in 1902 to Liverpool as a faculty member. In 1907 he moved to the University of London and, in 1913, at Edinburgh he began his investigations into the X rays discovered a few years earlier by Roent gen [774], Barkla noticed that X rays were scattered by gases and that the ex tent of scattering was proportional to the density of the gas and therefore to its molecular weight. From this he deduced that the more massive the atom, the greater the number of charged particles it contained, for the charged particles did the scattering. This was the first indi cation of a connection between the num ber of electrons in an atom and its posi tion in the periodic table, a move toward the concept of the atomic number. In 1904 Barkla further showed, from the manner in which X rays were scat tered, that they consisted of a particular kind of wave. They were transverse waves like those of light and not longitu dinal waves like those of sound, as Roentgen himself had thought. Barkla began his most important work in 1906. He showed that when X rays were scattered by particular elements, they produced a beam of characteristic penetrance. (At the time, there was no way of measuring the wavelength of X rays, so Barkla had to draw his deduc tions from the amount of absorption of a particular beam by an aluminum sheet of standard thickness.) If the elements were studied according to their order in the periodic table, the “characteristic X rays” they produced were more and more penetrating. It was these charac teristic X rays that Moseley [1121] soon used to bring the notion of the atomic number to completion. Barkla went on to recognize two types of such X rays, a more penetrating set which he called K radiation and a less penetrating set which he called L radia tion. This was the first step toward learn ing the distribution of electrons within the atom, a matter which Siegbahn [1111] and Bohr [1101] were soon to illuminate. For his work on X rays Barkla was awarded the 1917 Nobel Prize in phys ics. [1050] BEEBE, Charles William (bee'- bee) American naturalist Born: Brooklyn, New York, July 29, 1877 Died: Simla Research Station, near Arima, Trinidad, June 4, 1962 662 [1050] BEEBE
ASTON [1051] Beebe graduated from Columbia Uni versity in 1898 and then in 1899 began work at the New York Zoological Gar dens in the Bronx. He was particularly interested in birds and built up one of the finest ornithological collections in the world. As a youngster he had been fas cinated by the extraordinary voyages of Jules Verne (he was by no means the only scientist who received an initial in spiration from science fiction) and he engaged in a lifetime of extraordinary voyages of his own. He served as a combat aviator during World War I, traveled all over the world, and wrote fascinating books about his experiences. While modem naturalists from Linnaeus [276] to Andrews [1091] have achieved fame through their wan derings over the face of the earth, Beebe’s chief renown came with a jour ney of less than a mile—straight down. The desire to probe deeply in the ocean arose out of his interest in corals, which he wanted to study in their native haunts. Divers, however well protected, can only go down a few hundred feet be neath sea level. Submarines can do little better. Beebe decided, however, to build a shell of thick metal and conquer the pressures of the deep by brute force. He had to sacrifice maneuverability and be content to dangle from a surface ship (and if the cable holding his shell were to break, that would be the end). Such a shell of steel, with thick quartz windows, was built in the early 1930s. President Franklin D. Roosevelt, a friend of Beebe’s, helped to design the device, suggesting a spherical shape as opposed to Beebe’s original desire for a cylinder. In 1934 Beebe and a companion, Otis Barton, descended to a record depth of 3028 feet, well over half a mile. The dive, made near Bermuda, was the first penetration by man of depths beyond the surface layer of the ocean. The steel sphere was called a bathysphere (“sphere of the deep”). Beebe did not think his trip had proved of much scientific value and abandoned such attempts after making over thirty dives. However, he paved the way for Piccard’s [1092] bathyscaphe (“ship of the deep”), which a quarter of a century later was to make even more spectacular plunges into the depths. [1051] ASTON, Francis William English chemist and physicist Born: Harbome, near Birming ham, September 1, 1877 Died: Cambridge, November 20, 1945
Aston, the son of a merchant, finished high school at the top of his class in sci ence and mathematics in 1893 and went on to study chemistry at the University of Birmingham, where he worked under Frankland [655], In 1910 he went to Cambridge to work under J. J. Thomson [869], World War I (during which he served as an aeronautical engineer) in terrupted, but he returned in time to help Thomson in the latter’s experiments on deflecting positively charged ions in magnetic fields. These experiments made it appear that atoms of a particular ele ment might not all have the same weight, despite Dalton’s [389] original assumption of a century earlier. In order to decide the matter, Aston improved Thomson’s apparatus in 1919 and designed it so that all ions of a par ticular mass would focus in a fine line on the photographic film. Working with neon he showed that there were two lines, one indicating a mass of 20 and the other a mass of 22. From the com parative darkness of the two lines, Aston calculated that the ions of mass 20 were ten times as numerous as those of 22. If all the ions were lumped together they would have an average mass of 20.2 and that was, indeed, the atomic weight of neon. (Later, a third group of neon ions of mass 21, occurring in only tiny con centration, was discovered.) Working with chlorine Aston found two types of atoms, with masses of 35 and 37 in the ratio of 3 to 1. A weighted average came out to 35.5, which was the atomic weight of chlorine. By the end of 1920 it seemed quite clear to Aston that all atoms had masses that were very close to integers if the mass of hydrogen 663 [1051] ASTON
SODDY [1052] was taken as 1. The only reason that particular elements had atomic weights that were not integers was that they were mixtures of different atoms of different integral weights. Thus, the hypothesis first advanced by Prout [440] a century earlier was vindicated after all, as Mari- gnac [599] had foreseen it might be, al though it had been “killed” over and over again through the nineteenth cen tury. (Prout’s hypothesis had, indeed, been vindicated by Moseley’s [1121] atomic numbers the previous decade, but Aston’s work was the more direct evi dence.)
Aston’s mass spectrograph (so called because it divided the elements into lines like that of a spectroscope, with the different lines marking off differences in mass) showed that most stable elements were mixtures of isotopes, differing in mass but not in chemical properties. This strongly confirmed Soddy’s [1052] iso tope concept, which that physicist had been able to apply to radioactive ele ments only. Using his device, Aston was able to discover 212 of the 287 stable isotopes. A more refined mass spectrograph, built in 1925, enabled Aston to show that the “mass numbers” of the individ ual isotopes were actually very slightly different from integers, sometimes a little above, sometimes a little below. These slight mass discrepancies, it turned out, represented the energy that went into binding the component particles of the nucleus together and were called, by Harkins [1022], “packing fraction” or “binding energy.” When one type of atom was changed into another, the difference in binding energy could make itself felt in devastating fashion if enough atoms made the change. Two decades later, just such a wholesale change in atoms was found in connec tion with an isotope discovered by Dempster [1106], and the nuclear bomb was a reality. Aston was awarded the 1922 Nobel Prize in chemistry for his mass spec trograph and the knowledge it had given rise to. Unlike Ernest Rutherford [996], Aston envisaged a future in which the energy of the atom would be tapped by man, and in his Nobel acceptance speech he spoke of the dangers involved in such an eventuality. But such forethought re mained the province of only a few scien tists and science fiction writers. (Never theless, he lived just long enough—by three months—to see the dropping of the first nuclear bombs on Japanese cities.) Aston’s business acumen, by the way, had enabled him to accumulate a large estate which, on his death, he left, for the most part, to Trinity College. [1052] SODDY, Frederick English chemist Born: Eastbourne, Sussex, Sep tember 2, 1877 Died: Brighton, Sussex, Septem ber 22, 1956 After studying at Oxford and graduat ing in 1898 at the head of his class in chemistry, Soddy, the son of a merchant, went to Canada in 1899. There he worked under Ernest Rutherford [996] at McGill University. While there, he and Rutherford worked out an explana tion of radioactive disintegration. They suggested (as Boltwood [987] was also suggesting) that each radioactive ele ment, beginning with uranium or thorium, breaks down to form another element as it emits a subatomic particle. The new element in turn breaks down, and so on, until lead is formed. There are three series of such consecutive breakdowns now known. A fourth is possible, and although it does not exist in nature, it was created in the laboratory a generation after Soddy’s work. Soddy returned to England in 1902 and worked with Ramsay [832]. He then showed another facet of radioactive transformation, for he demonstrated spectroscopically that helium was formed in the course of uranium breakdown. In the process of radioactive disinte gration, some forty to fifty different ele ments (as judged by the difference in ra dioactive properties) were detected, and there were no more than ten or twelve places at the end of the periodic table 664 [1052] SODDY
JEANS [1053] where they could possibly be put. No chemist desired to throw out Mende- léev’s [705] extremely useful table, if that could possibly be avoided, so some way of allowing for the large number of in termediates had to be found. Soddy suggested that different ele ments produced in radioactive trans formations were capable of occupying the same place in the periodic table and on February 18, 1913, he called these el ements isotopes, from Greek words meaning “same place.” Furthermore, he indicated the positions in which individ ual isotopes might be found by suggest ing that the emission of an alpha particle causes the emitting element to become a new element with an atomic number decreased by two. The emission of a beta particle raises the atomic number by one. In this way, all the radioactive interme diates could be placed. In the next few years it became quite clear that isotopes were really different versions of a single chemical element. The isotopes differed in the mass of the nucleus and therefore had different ra dioactive characteristics (since these de pended on the nature of the nucleus). On the other hand, all isotopes of a par ticular element had the same number of electrons in the outer regions of the atom and so had the same chemical properties (since these depended on the number and distribution of the electrons of the atom). By 1914 Soddy had demonstrated quite conclusively that lead was the final stable element into which the radioactive intermediates were converted. (Boltwood had suggested this might be so a decade before.) It turned out that lead found in rocks that contained uranium or thorium did not have the same atomic weight as lead found in nonradioactive rocks. This was shown clearly by T. W. Richards [968]. The different samples of lead were the same chemically, and this pointed up the fact that isotopes differed in the mass of the atom but not in the chemical properties. Within five years the existence of iso topes in many elements that were neither radioactive nor formed by radioactivity was shown by J. J. Thomson [869] and, particularly, by Aston [1051]. For his discovery of isotopes Soddy was awarded the 1921 Nobel Prize in chemistry. He had accepted a profes sorship at Oxford two years earlier, and there he remained until his retirement in 1936. The retirement was brought on at a relatively early age through his grief at the death of his wife. Also, he did not get on well at the university, for he was not apparently a very tactful person. He was enraged by the abomination of World War I and, in particular, by the death of Moseley [1121] and developed radical ideas in consequence. As an ex ample, he was a firm believer in odd eco nomic theories such as Solvay’s [735] technocracy and wrote angry books on the subject. [1053] JEANS, Sir James Hopwood English mathematician and as tronomer
Born: Ormskirk, Lancashire, Sep tember 11, 1877 Died: Dorking, Surrey, Septem ber 17, 1946 Jeans, the son of a journalist, was a precocious, unhappy child, interested in clocks. He was second in his class in mathematics at Cambridge. After gradu ation in 1898 he taught mathematics there and from 1905 to 1909 lectured at Princeton University in the United States.
Jeans applied his mathematics to as tronomy with fruitful results. He studied the behavior of rapidly spinning bodies and, in particular, their methods of breaking up under the stress of centrif ugal force. He showed that the nebular hypothesis of Laplace [347] was untena ble, at least in the form presented by the French astronomer a century before. The nebular hypothesis had, in any case, been under attack for some time because, for one thing, the planets con tain 98 percent of the angular momen tum of the solar system. (To put it as simply as possible, the planets move rap idly in their orbits while the sun rotates 665 [1053] JEANS
AVERY [1054] rather slowly.) If the solar system had begun as a whirling cloud of gas, how could all that circular or near circular motion be concentrated in the outer edges that became the planets, and so lit tle reserved for the large central mass that became the sun? Chamberlin [766] had suggested that the sun had had a close encounter with a passing star and that the debris lifted into space by the mutual gravitational at traction had formed the planets. He had made some attempt to make this account for the distribution of angular momen tum, but it was Jeans in 1917 who ad vanced the most detailed analysis. The passing star, according to Jeans, had drawn a huge cigar-shaped lump of matter out of the sun. As the invader passed, its gravitational attraction gave the cigar-shaped matter a sideways pull, imparting to it a great deal of angular momentum. The thick part of the cigar produced the large planets Jupiter and Saturn, while the outer parts produced the smaller planets beyond and within the orbits of the two giants. This theory maintained popularity for a generation. Since near collisions of two stars are extremely unlikely because of the vast distance between stars, such a theory of planetary origins would indi cate that solar systems were very rare. In fact, it seemed quite likely that our sun (and the invader) might be the only stars in our galaxy to possess a planetary system.
However, a new version of the nebular hypothesis arose out of the shambles that Jeans had made of Laplace’s suggestion. The new version was presented along new and more sophisticated lines by men like Weizsäcker [1376] in the last couple of years of Jeans’s life. Contemporary thought, which quite discredits the vari ous theories of catastrophic origin of the solar system, would make it seem that planetary systems are common indeed. In 1928, the year in which he was knighted, Jeans speculated that matter was constantly being formed (at a very slow rate) in the universe. This specula tion was to be elevated into a serious theory by men like Gold [1437] and Hoyle [1398], From 1919 to 1929 Jeans was secre tary of the Royal Society and in 1934 he was appointed professor of astronomy at the Royal Institution in London. How ever, Jeans was known more for his writ ings on astronomy for the layman than for his serious contributions to the sub ject. From 1928 he devoted himself en tirely to such writings. His most popular books, perhaps, were The Universe Around Us (1929) and Through Space and Time (1934). [1054] AVERY, Oswald Theodore Canadian-American physician
tober 21, 1877 Died: Nashville, Tennessee, Feb ruary 20, 1955 Avery, the son of a clergyman who emigrated to the United States in 1887, obtained his medical degree from Co lumbia University in 1904 and joined the staff of the Rockefeller Institute (now Rockefeller University) in New York in 1913. His field of research involved the pneumococci—the pneumonia-causing bacteria. Bacteriologists had been study ing two different strains of pneumococci grown in the laboratory—one with a smooth coat (S), and the other lacking the coat and therefore rough in appear ance (R). Apparently the R strain lacked some enzyme needed to make the carbohydrate capsule. It was discovered that if an extract of the S strain was mixed with live R strain and the whole injected into a mouse, the mouse’s tissue would eventually contain live S strain. The S extract (thoroughly nonliving) ap parently contained a factor of some sort that supplied the necessary enzyme to the R strain and converted it into an S strain.
Everyone was sure the factor was pro tein in nature. In 1944, however, Avery and his associates studied the S extract and were able to show that the factor was pure deoxyribonucleic acid (DNA) and that no protein was present. This was a key development. Until then, DNA had been thought to be a relatively Download 17.33 Mb. Do'stlaringiz bilan baham: |
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