The 100 Most Influential Scientists of All Time (16 page)

Smallpox was widespread in the 18th century, and occasional outbreaks of special intensity resulted in a very high death rate. The disease, a leading cause of death at the time, respected no social class, and disfigurement was not uncommon in patients who recovered. The only means of combating smallpox was a primitive form of vaccination called variolation—intentionally infecting a healthy person with the “matter” taken from a patient sick with a mild attack of the disease. The practice, which originated in China and India, was based on two distinct concepts: first, that one attack of smallpox effectively protected against any subsequent attack and, second, that a person deliberately infected with a mild case of the disease would safely acquire such protection. It was, in present-day terminology, an “elective” infection—i.e., one given to a person in good health. Unfortunately, the transmitted disease did not always remain mild, and mortality sometimes
occurred. Furthermore, the inoculated person could disseminate the disease to others and thus act as a focus of infection.

Jenner had been impressed by the fact that a person who had suffered an attack of cowpox—a relatively harmless disease that could be contracted from cattle—could not take the smallpox—i.e., could not become infected whether by accidental or intentional exposure to smallpox. Pondering this phenomenon, Jenner concluded that cowpox not only protected against smallpox but could be transmitted from one person to another as a deliberate mechanism of protection.

The story of the great breakthrough is well known. In May 1796 Jenner found a young dairymaid, Sarah Nelmes, who had fresh cowpox lesions on her hand. On May 14, using matter from Sarah's lesions, he inoculated an eight-year-old boy, James Phipps, who had never had smallpox. Phipps became slightly ill over the course of the next 9 days but was well on the 10th. On July 1 Jenner inoculated the boy again, this time with smallpox matter. No disease developed; protection was complete. In 1798 Jenner, having added further cases, published privately a slender book entitled
An Inquiry into the Causes and Effects of the Variolae Vaccinae
. The procedure spread rapidly to America and the rest of Europe and soon was carried around the world.

Despite errors and occasional chicanery, the death rate from smallpox plunged. Jenner received worldwide recognition and many honours, but he made no attempt to enrich himself through his discovery and actually devoted so much time to the cause of vaccination that his private practice and personal affairs suffered severely. Parliament voted him a sum of £10,000 in 1802 and a further sum of £20,000 in 1806. Jenner not only received honours but also aroused opposition and found himself subjected to attacks and calumnies, despite which he continued his
activities on behalf of vaccination. His wife, ill with tuberculosis, died in 1815, and Jenner retired from public life.

(b. Sept. 5 or 6, 1766, Eaglesfield, Cumberland, Eng.—d. July 27, 1844, Manchester)

E
nglish meteorologist and chemist John Dalton was a pioneer in the development of modern atomic theory.

In 1793 Dalton published a collection of essays,
Meteorological Observations and Essays
, on meteorologic topics based on his own observations together with those of his friends John Gough and Peter Crosthwaite. It created little stir at first but contained original ideas that, together with Dalton's more developed articles, marked the transition of meteorology from a topic of general folklore to a serious scientific pursuit.

Dalton upheld the view, against contemporary opinion, that the atmosphere was a physical mixture of approximately 80 percent nitrogen and 20 percent oxygen rather than being a specific compound of elements. He measured the capacity of the air to absorb water vapour and the variation of its partial pressure with temperature. He defined partial pressure in terms of a physical law whereby every constituent in a mixture of gases exerted the same pressure it would have if it had been the only gas present. One of Dalton's contemporaries, the British scientist John Frederic Daniell, later hailed him as the “father of meteorology.”

Soon after the publication of the essays, Dalton wrote a description of the defect he had discovered in his own and his brother's vision. This paper was the first
publication on colour blindness, which for some time thereafter was known as Daltonism.

By far Dalton's most influential work in chemistry was his atomic theory. Attempts to trace precisely how Dalton developed this theory have proved futile; even Dalton's own recollections on the subject are incomplete. He based his theory of partial pressures on the idea that only like atoms in a mixture of gases repel one another, whereas unlike atoms appear to react indifferently toward each other. This conceptualization explained why each gas in a mixture behaved independently. Although this view was later shown to be erroneous, it served a useful purpose in allowing him to abolish the idea, held by many previous atomists from the Greek philosopher Democritus to the 18th-century mathematician and astronomer Ruggero Giuseppe Boscovich, that atoms of all kinds of matter are alike. Dalton claimed that atoms of different elements vary in size and mass, and indeed this claim is the cardinal feature of his atomic theory. He focused upon determining the relative masses of each different kind of atom, a process that could be accomplished, he claimed, only by considering the number of atoms of each element present in different chemical compounds.

Although Dalton had taught chemistry for several years, he had not yet performed actual research in this field. In a memoir read to the Manchester Literary and Philosophical Society on Oct. 21, 1803, he claimed: “An inquiry into the relative weights of the ultimate particles of bodies is a subject, as far as I know, entirely new; I have lately been prosecuting this inquiry with remarkable success.” He described his method of measuring the masses of various elements, including hydrogen, oxygen, carbon,
and nitrogen, according to the way they combined with fixed masses of each other. If such measurements were to be meaningful, the elements had to combine in fixed proportions. His measurements, crude as they were, allowed him to formulate the Law of Multiple Proportions: When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers. Thus, taking the elements as
A
and
B
, various combinations between them naturally occur according to the mass ratios
A:B = x:y
or
x:2y
or 2
x
:y, and so on. Different compounds were formed by combining atomic building blocks of different masses. As the Swedish chemist Jöns Jacob Berzelius wrote to Dalton: “The law of multiple proportions is a mystery without the atomic theory.” And Dalton provided the basis for this theory.

The problem remained, however, that a knowledge of ratios was insufficient to determine the actual number of elemental atoms in each compound. For example, methane was found to contain twice as much hydrogen as ethylene. Following Dalton's rule of “greatest simplicity,” namely, that
AB
is the most likely combination for which he found a meretricious justification in the geometry of close-packed spheres, he assigned methane a combination of one carbon and two hydrogen atoms and ethylene a combination of one carbon and one hydrogen atom. This is now known to be incorrect because the methane molecule is chemically symbolized as CH
₄
and the ethylene molecule as C
₂
H
₄
. Nevertheless, Dalton's atomic theory triumphed over its weaknesses because his foundational argument was correct. However, overcoming the defects of Dalton's theory was a gradual process, finalized in 1858 only after the Italian chemist Stanislao Cannizzaro pointed out the utility of Amedeo Avogadro's hypothesis in determining molecular masses. Since then, chemists have shown
the theory of Daltonian atomism to be a key factor underlying further advances in their field. Organic chemistry in particular progressed rapidly once Dalton's theory gained acceptance. Dalton's atomic theory earned him the sobriquet “father of chemistry.”

(b. Aug. 23, 1769, Montbéliard, France—d. May 13, 1832, Paris)

F
rench zoologist and statesman Baron Georges Cuvier established the sciences of comparative anatomy and paleontology. From 1784 to 1788 Cuvier attended the Académie Caroline (Karlsschule) in Stuttgart, Ger., where he studied comparative anatomy and learned to dissect. After graduation Cuvier served in 1788–95 as a tutor, during which time he wrote original studies of marine invertebrates, particularly the mollusks. His notes were sent to Étienne Geoffroy Saint-Hilaire, a professor of zoology at the Museum of Natural History in Paris, and at Geoffroy's urging Cuvier joined the staff of the museum. For a time the two scientists collaborated, and in 1795 they jointly published a study of mammalian classification, but their views eventually diverged.

Cuvier remained at the museum and continued his research in comparative anatomy. His first result, in 1797, was
Tableau élémentaire de l'histoire naturelle des animaux
(“Elementary Survey of the Natural History of Animals”), a popular work based on his lectures. In 1800–05, he published his
Leçons d'anatomie comparée
(“Lessons on Comparative Anatomy”). In this work, based also on his lectures at the museum, he put forward his principle of the “correlation of parts,” according to which the anatomical structure of every organ is functionally related to all other organs in the body of an animal, and the functional and structural characteristics of organs result from their
interaction with their environment. Moreover, according to Cuvier, the functions and habits of an animal determine its anatomical form, in contrast to Geoffroy, who held the reverse theory—that anatomical structure preceded and made necessary a particular mode of life.

Cuvier also argued that the anatomical characteristics distinguishing groups of animals are evidence that species had not changed since the Creation. Each species is so well coordinated, functionally and structurally, that it could not survive significant change. He further maintained that each species was created for its own special purpose and each organ for its special function. In denying evolution, Cuvier disagreed with the views of his colleague Jean-Baptiste Lamarck, who published his theory of evolution in 1809, and eventually also with Geoffroy, who in 1825 published evidence concerning the evolution of crocodiles.

While continuing his zoological work at the museum, Cuvier served as imperial inspector of public instruction and assisted in the establishment of French provincial universities. For these services he was granted the title “chevalier” in 1811. He also wrote the
Rapport historique sur les progrès des sciences naturelles depuis 1789, et sur leur état actuel
(“Historical Report on the Progress of the Sciences”), published in 1810. These publications are lucid expositions of the European science of his time.

Meanwhile, Cuvier also applied his views on the correlation of parts to a systematic study of fossils that he had excavated. He reconstructed complete skeletons of unknown fossil quadrupeds. These constituted astonishing new evidence that whole species of animals had become extinct. Furthermore, he discerned a remarkable sequence in the creatures he exhumed. The deeper, more remote strata contained animal remains—giant salamanders, flying reptiles, and extinct elephants—that were far less
similar to animals now living than those found in the more recent strata. He summarized his conclusions, first in 1812 in his
Recherches sur les ossements fossiles de quadrupèdes
(“Researches on the Bones of Fossil Vertebrates”), which included the essay “Discours préliminaire” (“Preliminary Discourse”), as well as in the expansion of this essay in book form in 1825,
Discours sur les révolutions de la surface du globe
(“Discourse on the Revolutions of the Globe”).

Cuvier's work gave new prestige to the old concept of catastrophism according to which a series of “revolutions,” or catastrophes—sudden land upheavals and floods—had destroyed entire species of organisms and carved out the present features of the Earth. He believed that the area laid waste by these spectacular paroxysms, of which Noah's flood was the most recent and dramatic, was sometimes repopulated by migration of animals from an area that had been spared. Catastrophism remained a major geologic doctrine until it was shown that slow changes over long periods of time could explain the features of the Earth.

In 1817 Cuvier published
Le Règne animal distribué d'après son organisation
(“The Animal Kingdom, Distributed According to Its Organization”), which, with its many subsequent editions, was a significant advance over the systems of classification established by Linnaeus. Cuvier showed that animals possessed so many diverse anatomical traits that they could not be arranged in a single linear system. Instead, he arranged animals into four large groups of animals (vertebrates, mollusks, articulates, and radiates), each of which had a special type of anatomical organization. All animals within the same group were classified together, as he believed they were all modifications of one particular anatomical type. Although his classification is no longer used, Cuvier broke away from the 18th-century idea that all living things were arranged in a continuous series from the simplest up to man.

Cuvier's lifework may be considered as marking a transition between the 18th-century view of nature and the view that emerged in the last half of the 19th century as a result of the doctrine of evolution. By rejecting the 18th-century method of arranging animals in a continuous series in favour of classifying them in four separate groups, he raised the key question of why animals were anatomically different. Although Cuvier's doctrine of catastrophism did not last, he did set the science of palaeontology on a firm, empirical foundation. He did this by introducing fossils into zoological classification, showing the progressive relation between rock strata and their fossil remains, and by demonstrating, in his comparative anatomy and his reconstructions of fossil skeletons, the importance of functional and anatomical relationships.