The 100 Most Influential Scientists of All Time (27 page)

It was Michelson's intention to use the interferometer to measure the Earth's velocity against the “ether” that was then thought to make up the basic substratum of the universe. If the Earth were traveling through the light-conducting ether, then the speed of the light traveling in the same direction would be expected to be equal to the velocity of light plus the velocity of the Earth, whereas the speed of light traveling at right angles to the Earth's path would be expected to travel only at the velocity of light. His earliest experiments in Berlin showed no interference fringes, however, which seemed to signify that there was no difference in the speed of the light rays and, therefore, no Earth motion relative to the ether.

In 1883 he accepted a position as professor of physics at the Case School of Applied Science in Cleveland and there concentrated his efforts on improving the delicacy of his interferometer experiment. By 1887, with the help of his colleague, American chemist Edward Williams Morley, he was ready to announce the results of what has since come to be called the Michelson-Morley experiment. Those results were still negative; there were no interference fringes and apparently no motion of the Earth relative to the ether.

It was perhaps the most significant negative experiment in the history of science. In terms of classical Newtonian physics, the results were paradoxical. Evidently, the speed of light plus any other added velocity was still equal only to the speed of light. To explain the result of the Michelson-Morley experiment, physics had to be recast on a new and more refined foundation, something that resulted, eventually, in Albert Einstein's formulation of the theory of relativity in 1905.

In 1892 Michelson, after serving as professor of physics at Clark University at Worcester, Mass., from 1889, was appointed professor and the first head of the department of physics at the newly organized University of Chicago, a position he held until his retirement in 1929. From 1923 to 1927 he served as president of the National Academy of Sciences. In 1907 he became the first American ever to receive a Nobel Prize in the sciences, for his spectroscopic and metrological investigations, the first of many honours he was to receive.

Michelson advocated using some particular wavelength of light as a standard of distance (a suggestion generally accepted in 1960) and, in 1893, measured the standard metre in terms of the red light emitted by heated cadmium. His interferometer made it possible for him to determine the width of heavenly objects by matching the light rays from the two sides and noting the interference fringes that resulted. In 1920, using a 6-metre (20-foot) interferometer attached to a 254-centimetre (100-inch) telescope, he succeeded in measuring the diameter of the star Betelgeuse (Alpha Orionis) as 386,160,000 km (300 times the diameter of the Sun). This was the first substantially accurate determination of the size of a star.

In 1923 Michelson returned to the problem of the accurate measurement of the velocity of light. In the California mountains he surveyed a 35-kilometre pathway between
two mountain peaks, determining the distance to an accuracy of less than 2.5 cm. He made use of a special eight-sided revolving mirror and obtained a value of 299,798 km/sec for the velocity of light. To refine matters further, he made use of a long, evacuated tube through which a light beam was reflected back and forth until it had traveled 16 km through a vacuum. Michelson died before the results of his final tests could be evaluated, but in 1933 the final figure was announced as 299,774 km/sec, a value less than 2 km/sec higher than the value accepted in the 1970s.

(b. Dec. 11, 1843, Clausthal, Hannover [now Clausthal-Zellerfeld, Ger.]—d. May 27, 1910, Baden-Baden, Ger.)

G
erman physician Robert Heinrich Hermann Koch was one of the founders of bacteriology. He discovered the anthrax disease cycle (1876) and the bacteria responsible for tuberculosis (1882) and cholera (1883). For his discoveries in regard to tuberculosis, he received the Nobel Prize for Physiology or Medicine in 1905.

Koch's career began with his research on anthrax. He cultivated anthrax organisms in suitable media on microscope slides, demonstrated their growth into long filaments, and discovered the formation within them of oval, translucent bodies—dormant spores. Koch found that the dried spores could remain viable for years, even under exposed conditions. The finding explained the recurrence of the disease in pastures long unused for grazing, for the dormant spores could, under the right conditions, develop into the rod-shaped bacteria (bacilli) that cause anthrax. The anthrax life cycle, which Koch had discovered, was announced and
illustrated at Breslau in 1876, on the invitation of Ferdinand Cohn, an eminent botanist. Julius Cohnheim, a famous pathologist, was deeply impressed by Koch's presentation. “It leaves nothing more to be proved,” he said.

Koch worked out the details of his pure-culture techniques a few years later. That a disease organism might be cultured outside the body was a concept introduced by Louis Pasteur, but the pure-culture techniques for doing so were perfected by Koch, whose precise and ingenious experiments demonstrated the complete life cycle of an important organism. The anthrax work afforded for the first time convincing proof of the definite causal relation of a particular microorganism to a particular disease.

In 1877 Koch published an important paper on the investigation, preservation, and photographing of bacteria. His work was illustrated by superb photomicrographs. In his paper he described his method of preparing thin layers of bacteria on glass slides and fixing them by gentle heat. Koch also invented the apparatus and the procedure for the very useful hanging-drop technique, whereby microorganisms could be cultured in a drop of nutrient solution on the underside of a glass slide.

In 1878 Koch summarized his experiments on the etiology of wound infection. By inoculating animals with material from various sources, he produced six types of infection, each caused by a specific microorganism. He then transferred these infections by inoculation through several kinds of animals, reproducing the original six types. In that study, he observed differences in pathogenicity for different species of hosts and demonstrated that the animal body is an excellent apparatus for the cultivation of bacteria.

Koch, now recognized as a scientific investigator of the first rank, obtained a position in Berlin in the Imperial Health Office, where he set up a laboratory in bacteriology. With his collaborators, he devised new research methods to isolate pathogenic bacteria. Koch determined guidelines to prove that a disease is caused by a specific organism. These four basic criteria, called Koch's postulates, are:

• A specific microorganism is always associated with a given disease.

• The microorganism can be isolated from the diseased animal and grown in pure culture in the laboratory.

• The cultured microbe will cause disease when transferred to a healthy animal.

• The same type of microorganism can be isolated from the newly infected animal.

Koch concentrated his efforts on the study of tuberculosis, with the aim of isolating its cause. Although it was suspected that tuberculosis was caused by an infectious agent, the organism had not yet been isolated and identified. By modifying the method of staining, Koch discovered the tubercle bacillus and established its presence in the tissues of animals and humans suffering from the disease. A fresh difficulty arose when for some time it proved impossible to grow the organism in pure culture. But eventually Koch succeeded in isolating the organism in a succession of media and induced tuberculosis in animals by inoculating them with it. Its etiologic role was thereby established. On March 24, 1882, Koch announced before the Physiological Society of Berlin that he had isolated
and grown the tubercle bacillus, which he believed to be the cause of all forms of tuberculosis.

Meanwhile, Koch's work was interrupted by an outbreak of cholera in Egypt and the danger of its transmission to Europe. As a member of a German government commission, Koch went to Egypt to investigate the disease. Although he soon had reason to suspect a particular comma-shaped bacterium (vibrio) as the cause of cholera, the epidemic ended before he was able to confirm his hypothesis. Nevertheless, he raised awareness of amebic dysentery and differentiated two varieties of Egyptian conjunctivitis. Proceeding to India, where cholera is endemic, he completed his task, identifying both the organism responsible for the disease and its transmission via drinking water, food, and clothing.

Resuming his studies of tuberculosis, Koch investigated the effect an injection of dead bacilli had on a person who subsequently received a dose of living bacteria and concluded that he may have discovered a cure for the disease. In his studies he used as the active agent a sterile liquid produced from cultures of the bacillus. However, the liquid, which he named tuberculin (1890), proved disappointing, and sometimes dangerous, as a curative agent. Consequently, its importance as a means of detecting a present or past tubercular state was not immediately recognized. Additional work on tuberculosis came later, but, after the seeming debacle of tuberculin, Koch was also occupied with a great variety of investigations into diseases of humans and animals—studies of leprosy, bubonic plague, livestock diseases, and malaria.

In 1901 Koch reported work done on the pathogenicity of the human tubercle bacillus in domestic animals. He believed that infection of human beings by bovine tuberculosis is so rare that it is not necessary to take any measures against it. That conclusion was rejected
by commissions of inquiry in Europe and America but extensive and important work was stimulated by Koch. As a result, successful measures of prophylaxis were devised.

(b. May 6, 1856, Freiberg, Moravia, Austrian Empire [now Příbor, Czech Republic]—d. Sept. 23, 1939, London, Eng.)

A
ustrian neurologist Sigmund Freud was the founder of psychoanalysis. Freud may justly be called the most influential intellectual legislator of his age. His creation of psychoanalysis was at once a theory of the human psyche, a therapy for the relief of its ills, and an optic for the interpretation of culture and society. Despite repeated criticisms, attempted refutations, and qualifications of Freud's work, its spell remained powerful well after his death and in fields far removed from psychology as it is narrowly defined. If, as the American sociologist Philip Rieff once contended, “psychological man” replaced such earlier notions as political, religious, or economic man as the 20th century's dominant self-image, it is in no small measure due to the power of Freud's vision and the seeming inexhaustibility of the intellectual legacy he left behind.

In Freud's writing “Entwurf einer Psychologie” (“Project for a Scientific Psychology”), written in 1895 and published in 1950, he affirmed his intention to find a physiological and materialist basis for his theories of the psyche. In late 1885 Freud went to the Salpêtrière clinic in Paris, where he worked under the guidance of Jean-Martin Charcot. His 19 weeks in the French capital proved a turning point in his career, for Charcot's work with patients classified as “hysterics” introduced Freud to the possibility that
psychological disorders might have their source in the mind rather than the brain.

Freud later developed a partnership with the physician Josef Breuer after his return to Vienna from Paris. Freud turned to a clinical practice in neuropsychology, and the office he established at Berggasse 19 was to remain his consulting room for almost half a century. Before their collaboration began, during the early 1880s, Breuer had treated a patient named Bertha Pappenheim—or “Anna O.,” as she became known in the literature—who was suffering from a variety of hysterical symptoms. Rather than using hypnotic suggestion, as had Charcot, Breuer allowed her to lapse into a state resembling autohypnosis, in which she would talk about the initial manifestations of her symptoms. To Breuer's surprise, the very act of verbalization seemed to provide some relief from their hold over her (although later scholarship has cast doubt on its permanence). “The talking cure” or “chimney sweeping,” as Breuer and Anna O., respectively, called it, seemed to act cathartically to produce an abreaction, or discharge, of the pent-up emotional blockage at the root of the pathological behaviour.