The 100 Most Influential Scientists of All Time (20 page)

Many remaining problems in the specification of minerals were resolved by the law of isomorphism, the recognition that chemically similar substances possess similar crystal forms, discovered in 1818 by the German chemist Eilhardt Mitscherlich. Berzelius had provided both the patronage and the foundational concepts for
Mitscherlich's own career. Ultimately, Berzelius transformed the field and established a flourishing tradition of chemical mineralogy.

Organic chemistry also posed problems in the discrimination between substances. In 1814 Berzelius again turn his attention to organic analysis. At this point, he isolated stoichiometric compounds and worked to determine their elemental constituents. Berzelius argued that, despite differences between organic and inorganic matter, organic compounds could be assigned a dualistic composition and therefore could be specified in the same manner as inorganic ones. The application of his precept that organic chemistry could be understood in terms of the principles that govern inorganic chemistry reached its zenith in the 1830s, especially as it was embodied in the older theory of radicals. However, it was also at this time that younger chemists discovered phenomena such as chlorine substitution and began to recast inorganic chemistry in the light of organic substances.

Among Berzelius's other accomplishments were his improvements of laboratory apparatuses and techniques used for chemical and mineral analysis, especially solvent extraction, elemental analysis, quantitative wet chemistry, and qualitative mineral analysis. Berzelius also characterized and named two new concepts: “isomerism,” in which chemically diverse substances possess the same composition; and “catalysis,” in which certain chemical reactions are facilitated by the presence of substances that are themselves unaffected. He also coined the term
protein
while
attempting to apply a dualistic organic chemistry to the constituents of living things.

(b. April 26, 1785, Les Cayes, Saint-Domingue, West Indies [now in Haiti]—d. Jan. 27, 1851, New York, N.Y., U.S.)

J
ohn James Audubon, whose original name was Fougère Rabin, or Jean Rabin, was an ornithologist, artist, and naturalist who became particularly well known for his drawings and paintings of North American birds. The illegitimate son of a French merchant, planter, and slave trader and a Creole woman of Saint-Domingue, Audubon and his illegitimate half-sister (who was also born in the West Indies) were legalized by adoption in 1794, five years after their father returned to France.

Young Audubon developed an interest in drawing birds during his boyhood in France. At age 18 he was sent to the United States in order to avoid conscription and to enter business. He began his study of North American birds at that time; this study would eventually lead him from Florida to Labrador, Can. With Frederick Rozier, Audubon attempted to operate a mine, then a general store. The latter venture they attempted first in Louisville, Ky., later in Henderson, Ky., but the partnership was dissolved after they failed utterly. Audubon then attempted some business ventures in partnership with his brother-in-law; these, too, failed. By 1820 he had begun to take what jobs he could to provide a living and to concentrate on his steadily growing interest in drawing birds; he worked for a time as a taxidermist, later making portraits and teaching drawing, while his wife worked as a governess.

By 1824 he began to consider publication of his bird drawings, but he was advised to seek a publisher in Europe, where he would find better engravers and greater interest
in his subject. In 1826 he went to Europe in search of patrons and a publisher. He was well received in Edinburgh and, after the king subscribed for his books, in London as well. The engraver Robert Havell of London undertook publication of his illustrations as
The Birds of America
, 4 vol. (435 hand-coloured plates, 1827–38). William MacGillivray helped write the accompanying text,
Ornithological Biography
, 5 vol. (octavo, 1831–39), and
A Synopsis of the Birds of North America
, 1 vol. (1839), which serves as an index. Until 1839 Audubon divided his time between Europe and the United States, gathering material, completing illustrations, and financing publication through subscription. His reputation established, Audubon then settled in New York City and prepared a smaller edition of his
Birds of America
, 7 vol. (octavo, 1840–44), and a new work,
Viviparous Quadrupeds of North America
, 3 vol. (150 plates, 1845–48), and the accompanying text (3 vol., 1846–53), completed with the aid of his sons and the naturalist John Bachman.

Critics of Audubon's work have pointed to certain fanciful (or even impossible) poses and inaccurate details, but few argue with their excellence as art. To many, Audubon's work far surpasses that of his contemporary (and more scientific) fellow ornithologist, Alexander Wilson.

(b. Sept. 22, 1791, Newington, Surrey, Eng.—d. Aug. 25, 1867, Hampton Court)

E
nglish physicist and chemist Michael Faraday is known for his many experiments that contributed greatly to the understanding of electromagnetism. Faraday, who became one of the greatest scientists of the 19th century, began his career as a chemist. He wrote a manual of practical chemistry that reveals his mastery of the technical aspects of his art, discovered a number of new organic
compounds, among them benzene, and was the first to liquefy a “permanent” gas (i.e., one that was believed to be incapable of liquefaction). His major contribution, however, was in the field of electricity and magnetism. He was the first to produce an electric current from a magnetic field, invented the first electric motor and dynamo, demonstrated the relation between electricity and chemical bonding, discovered the effect of magnetism on light, and discovered and named diamagnetism, the peculiar behaviour of certain substances in strong magnetic fields. He provided the experimental, and a good deal of the theoretical, foundation upon which James Clerk Maxwell erected classical electromagnetic field theory.

Faraday began his scientific career as Sir Humphry Davy's laboratory assistant. When Faraday joined Davy in 1812, Davy was in the process of revolutionizing the chemistry of the day. Davy's ideas were influenced by an atomic theory that was also to have important consequences for Faraday's thought. This theory, proposed in the 18th century by Ruggero Giuseppe Boscovich, argued that atoms were mathematical points surrounded by alternating fields of attractive and repulsive forces. One property of such atoms is that they can be placed under considerable strain, or tension, before the “bonds” holding them together are broken. These strains were to be central to Faraday's ideas about electricity.

Faraday's work under Davy came to an end in 1820. There followed a series of discoveries that astonished the scientific world. Faraday achieved his early renown as a chemist. In 1820 he produced the first known compounds of carbon and chlorine, C
₂
Cl
₆
and C
₂
Cl
₄
. These compounds were produced by substituting chlorine for hydrogen in “olefiant gas” (ethylene), the first substitution reactions induced. In 1825, as a result of research on illuminating gases, Faraday isolated and described benzene. In the 1820s he also conducted investigations of steel alloys, helping to lay the foundations for scientific metallurgy and metallography. While completing an assignment from the Royal Society of London to improve the quality of optical glass for telescopes, he produced a glass of very high refractive index that was to lead him, in 1845, to the discovery of diamagnetism.

By the 1820s André-Marie Ampère had shown that magnetic force apparently was a circular one, producing in effect a cylinder of magnetism around a wire carrying an electric current. No such circular force had ever before been observed, and Faraday was the first to understand what it implied. If a magnetic pole could be isolated, it ought to move constantly in a circle around a current-carrying wire. Faraday's ingenuity and laboratory skill enabled him to construct an apparatus that confirmed this conclusion. This device, which transformed electrical energy into mechanical energy, was the first electric motor.

On Aug. 29, 1831, Faraday wound a thick iron ring on one side with insulated wire that was connected to a battery. He then wound the opposite side with wire connected to a galvanometer. What he expected was that a “wave” would be produced when the battery circuit was closed and that the wave would show up as a deflection of the galvanometer in the second circuit. He closed the primary circuit and, to his delight and satisfaction, saw the galvanometer needle jump. A current had been induced in the secondary coil by one in the primary. When he opened the circuit, however, he was astonished to see the galvanometer jump in the opposite direction. Somehow, turning off the current also created an induced current in the secondary circuit, equal and opposite to the original current. This phenomenon led Faraday to propose what he called the “electrotonic” state of particles in the wire, which he considered a state of tension.

In the fall of 1831 Faraday attempted to determine just how an induced current was produced. He discovered that when a permanent magnet was moved in and out of a coil of wire a current was induced in the coil. Magnets, he knew, were surrounded by forces that could be made visible by the simple expedient of sprinkling iron filings on a card held over them. Faraday saw the “lines of force” thus
revealed as lines of tension in the medium, namely air, surrounding the magnet, and he soon discovered the law determining the production of electric currents by magnets: the magnitude of the current was dependent upon the number of lines of force cut by the conductor in unit time. He immediately realized that a continuous current could be produced by rotating a copper disk between the poles of a powerful magnet and taking leads off the disk's rim and centre. This was the first dynamo. It was also the direct ancestor of electric motors, for it was only necessary to reverse the situation, to feed an electric current to the disk, to make it rotate.

In 1832 Faraday began what promised to be a rather tedious attempt to prove that all electricities had precisely the same properties and caused precisely the same effects. The key effect was electrochemical decomposition. Voltaic and electromagnetic electricity posed no problems, but static electricity did. As Faraday delved deeper into the problem, he made two startling discoveries. First, electrical force did not, as had long been supposed, act at a distance upon chemical molecules to cause them to dissociate. It was the passage of electricity through a conducting liquid medium that caused the molecules to dissociate, even when the electricity merely discharged into the air and did not pass into a “pole” or “centre of action” in a voltaic cell. Second, the amount of the decomposition was found to be related in a simple manner to the amount of electricity that passed through the solution.

These findings led Faraday to a new theory of electrochemistry. The electric force, he argued, threw the molecules of a solution into a state of tension (his electrotonic state). When the force was strong enough to distort
the fields of forces that held the molecules together so as to permit the interaction of these fields with neighbouring particles, the tension was relieved by the migration of particles along the lines of tension, the different species of atoms migrating in opposite directions. The amount of electricity that passed, then, was clearly related to the chemical affinities of the substances in solution. These experiments led directly to Faraday's two laws of electrochemistry: (1) The amount of a substance deposited on each electrode of an electrolytic cell is directly proportional to the quantity of electricity passed through the cell. (2) The quantities of different elements deposited by a given amount of electricity are in the ratio of their chemical equivalent weights.

Faraday's work on electrochemistry provided him with an essential clue for the investigation of static electrical induction. Since the amount of electricity passed through the conducting medium of an electrolytic cell determined the amount of material deposited at the electrodes, why should not the amount of electricity induced in a nonconductor be dependent upon the material out of which it was made? In short, why should not every material have a specific inductive capacity? Every material does, and Faraday was the discoverer of this fact.