The 100 Most Influential Scientists of All Time (14 page)

Galvani followed his father's preference for medicine by attending the University of Bologna, graduating in 1759. On obtaining the doctor of medicine degree, with a thesis (1762)
De ossibus
on the formation and development of bones, he was appointed lecturer in anatomy at the University of Bologna and professor of obstetrics at the separate Institute of Arts and Sciences. Beginning with his doctoral thesis, his early research was in comparative anatomy—such as the structure of renal tubules, nasal mucosa, and the middle ear—with a tendency toward physiology, a direction appropriate to the later work for which he is noted.

Galvani's developing interest was indicated by his lectures on the anatomy of the frog in 1773 and in electrophysiology in the late 1770s, when, following the
acquisition of an electrostatic machine (a large device for making sparks) and a Leyden jar (a device used to store static electricity), he began to experiment with muscular stimulation by electrical means. His notebooks indicate that, from the early 1780s, animal electricity remained his major field of investigation. Numerous ingenious observations and experiments have been credited to him; in 1786, for example, he obtained muscular contraction in a frog by touching its nerves with a pair of scissors during an electrical storm. He also observed the legs of a skinned frog kick when a scalpel touched a lumbar nerve of the animal while an electrical machine was activated.

Galvani assured himself by further experiments that the twitching was, in fact, related to the electrical action. He also elicited twitching without the aid of the electrostatic machine by pressing a copper hook into a frog's spinal cord and hanging the hook on an iron railing. Although twitching could occur during a lightning storm or with the aid of an electrostatic machine, it also occurred with only a metallic contact between leg muscles and nerves leading to them. A metallic arc connecting the two tissues could therefore be a substitute for the electrostatic machine.

Galvani delayed the announcement of his findings until 1791, when he published his essay
De Viribus Electricitatis in Motu Musculari Commentarius (Commentary on the Effect of Electricity on Muscular Motion
). He concluded that animal tissue contained a heretofore neglected innate, vital force, which he termed “animal electricity,” which activated nerve and muscle when spanned by metal probes. He believed that this new force was a form of electricity in addition to the “natural” form that is produced by lightning or by the electric eel and torpedo ray and to the “artificial” form that
is produced by friction (i.e., static electricity). He considered the brain to be the most important organ for the secretion of this “electric fluid” and the nerves to be conductors of the fluid to the nerve and muscle, the tissues of which act as did the outer and inner surfaces of the Leyden jar. The flow of this electric fluid provided a stimulus for the irritable muscle fibres, according to his explanation.

Galvani's scientific colleagues generally accepted his views, but Alessandro Volta, the outstanding professor of physics at the University of Pavia, was not convinced by the analogy between the muscle and the Leyden jar. Deciding that the frog's legs served only as an indicating electroscope, he held that the contact of dissimilar metals was the true source of stimulation; he referred to the electricity so generated as “metallic electricity” and decided that the muscle, by contracting when touched by metal, resembled the action of an electroscope. Furthermore, Volta said that, if two dissimilar metals in contact both touched a muscle, agitation would also occur and increase with the dissimilarity of the metals. Thus Volta rejected the idea of an “animal electric fluid,” replying that the frog's legs responded to differences in metal temper, composition, and bulk. Galvani refuted this by obtaining muscular action with two pieces of the same material. Galvani's gentle nature and Volta's high principles precluded any harshness between them. Volta, who coined the term galvanism, said of Galvani's work that “it contains one of the most beautiful and most surprising discoveries.”

In retrospect, Galvani and Volta are both seen to have been partly right and partly wrong. Galvani was correct in attributing muscular contractions to an electrical stimulus but wrong in identifying it as an “animal electricity.” Volta correctly denied the existence of an “animal electricity” but was wrong in implying that every electrophysiological effect requires two different metals as sources of current.
Galvani, shrinking from the controversy over his discovery, continued his work as teacher, obstetrician, and surgeon, treating both wealthy and needy without regard to fee. In 1794 he offered a defense of his position in an anonymous book,
Dell'uso e dell'attività dell'arco conduttore nella contrazione dei muscoli
(“On the Use and Activity of the Conductive Arch in the Contraction of Muscles”), the supplement of which described muscular contraction without the need of any metal. He caused a muscle to contract by touching the exposed muscle of one frog with a nerve of another and thus established for the first time that bioelectric forces exist within living tissue.

Galvani provided the major stimulus for Volta to discover a source of constant current electricity; this was the voltaic pile, or a battery, with its principles of operation combined from chemistry and physics. This discovery led to the subsequent age of electric power. Moreover, Galvani opened the way to new research in the physiology of muscle and nerve and to the entire subject of electrophysiology.

(b. Nov. 15, 1738, Hanover, Ger.—d. Aug. 25, 1822, Slough, Buckinghamshire, Eng.)

G
erman-born British astronomer Sir William Herschel was the founder of sidereal astronomy for the systematic observation of the heavens. He discovered the planet Uranus, hypothesized that nebulae are composed of stars, and developed a theory of stellar evolution. He was knighted in 1816.

The intellectual curiosity that Herschel acquired from his father led him from the practice to the theory of music,
which he studied in Robert Smith's
Harmonics
. From this book he turned to Smith's
A Compleat System of Opticks
, which introduced him to the techniques of telescope construction. Herschel soon began to grind his own mirrors. They were ground from metal disks of copper, tin, and antimony in various proportions. He later produced large mirrors of superb quality—his telescopes proved far superior even to those used at the Greenwich Observatory. He also made his own eyepieces, the strongest with a magnifying power of 6,450 times. Herschel's largest instrument, too cumbersome for regular use, had a mirror made of speculum metal, with a diameter of 122 centimetres (48 inches) and a focal length of 12 metres (40 feet). Completed in 1789, it became one of the technical wonders of the 18th century.

In 1781, during his third and most complete survey of the night sky, Herschel came upon an object that he realized was not an ordinary star. It proved to be the planet Uranus, the first planet to be discovered since prehistoric times. Herschel became famous almost overnight. His friend Dr. William Watson, Jr., introduced him to the Royal Society of London, which awarded him the Copley Medal for the discovery of Uranus, and elected him a Fellow. He was subsequently appointed as an astronomer to George III.

Herschel's big telescopes were ideally suited to study the nature of nebulae, which appear as luminous patches in the sky. Some astronomers thought they were nothing more than clusters of innumerable stars the light of which blends to form a milky appearance. Others held that some nebulae were composed of a luminous fluid. However, Herschel found that his most powerful telescope could resolve into stars several nebulae that appeared “milky” to less well equipped observers. He was convinced that other nebulae would eventually be resolved into individual stars
with more powerful instruments. This encouraged him to argue in 1784 and 1785 that all nebulae were formed of stars and that there was no need to postulate the existence of a mysterious luminous fluid to explain the observed facts. Nebulae that could not yet be resolved must be very distant systems, he maintained; and, since they seem large to the observer, their true size must indeed be vast—possibly larger even than the star system of which the Sun is a member. By this reasoning, Herschel was led to postulate the existence of what later were called “island universes” of stars.

In order to interpret the differences between these star clusters, Herschel emphasized their relative densities by contrasting a cluster of tightly packed stars with others in which the stars were widely scattered. These formations showed that attractive forces were at work. In other words, a group of widely scattered stars was at an earlier stage of its development than one whose stars were tightly packed. Thus, Herschel made change in time, or evolution, a fundamental explanatory concept in astronomy.

In 1785 Herschel developed a cosmogony—a theory concerning the origin of the universe: the stars originally were scattered throughout infinite space, in which attractive forces gradually organized them into even more fragmented and tightly packed clusters. Turning then to the system of stars of which the Sun is part, he sought to determine its shape on the basis of two assumptions: (1) that with his telescope he could see all the stars in the system, and (2) that within the system the stars are regularly spread out. Both of these assumptions he subsequently had to abandon. But in his studies he gave the first major example of the usefulness of stellar statistics in that he
could count the stars and interpret this data in terms of the extent in space of the Galaxy's star system.

On Nov. 13, 1790, Herschel observed a remarkable nebula, which he was forced to interpret as a central star surrounded by a cloud of “luminous fluid.” This discovery contradicted his earlier views. Hitherto Herschel had reasoned that many nebulae that he was unable to resolve (separate into distinct stars), even with his best telescopes, might be distant “island universes” (such objects are now known as galaxies). He was able, however, to adapt his earlier theory to this new evidence by concluding that the central star he had observed was condensing out of the surrounding cloud under the forces of gravity. In 1811 he extended his cosmogony backward in time to the stage when stars had not yet begun to form out of the fluid.

In dealing with the structural organization of the heavens, Herschel assumed that all stars were equally bright, so that differences in apparent brightness are an index only of differences in distances. Throughout his career he stubbornly refused to acknowledge the accumulating evidence that contradicted this assumption. Herschel's labours through 20 years of systematic sweeps for nebulae (1783–1802) resulted in three catalogs listing 2,500 nebulae and star clusters that he substituted for the 100 or so milky patches previously known. He also cataloged 848 double stars—pairs of stars that appear close together in space, and measurements of the comparative brightness of stars. He observed that double stars did not occur by chance as a result of random scattering of stars in space but that they actually revolved about each other. His 70 published papers include not only studies of the motion of the solar system through space and the
announcement in 1800 of the discovery of infrared rays but also a succession of detailed investigations of the planets and other members of the solar system.

(b. Aug. 26, 1743, Paris, France—d. May 8, 1794, Paris)

A
ntoine-Laurent Lavoisier was a prominent French chemist and leading figure in the 18th-century chemical revolution who developed an experimentally based theory of the chemical reactivity of oxygen and coauthored the modern system for naming chemical substances. Having also served as a leading financier and public administrator before the French Revolution, he was executed with other financiers during the revolutionary terror.

The chemistry Lavoisier studied as a student was not a subject particularly noted for conceptual clarity or theoretical rigour. Although chemical writings contained considerable information about the substances chemists studied, little agreement existed upon the precise composition of chemical elements or between explanations of changes in composition. Many natural philosophers still viewed the four elements of Greek natural philosophy—earth, air, fire, and water—as the primary substances of all matter. Chemists like Lavoisier focused their attention upon analyzing “mixts” (i.e., compounds), such as the salts formed when acids combine with alkalis. They hoped that by first identifying the properties of simple substances they would then be able to construct theories to explain the properties of compounds.

Pneumatic chemistry was a lively subject at the time Lavoisier became interested in a particular set of problems
that involved air: the linked phenomena of combustion, respiration, and what 18th-century chemists called calcination (the change of metals to a powder [calx], such as that obtained by the rusting of iron).

The assertion that mass is conserved in chemical reactions was an assumption of Enlightenment investigators rather than a discovery revealed by their experiments. Lavoisier believed that matter was neither created nor destroyed in chemical reactions, and in his experiments he sought to demonstrate that this belief was not violated. Still he had difficulty proving that his view was universally valid. His insistence that chemists accepted this assumption as a law was part of his larger program for raising chemistry to the investigative standards and causal explanation found in contemporary experimental physics.