The 100 Most Influential Scientists of All Time (29 page)

As time went on physicists recognized ever more clearly that—because Planck's constant was not zero but
had a small but finite value—the microphysical world, the world of atomic dimensions, could not in principle be described by ordinary classical mechanics.

In 1905, independently of Planck's work, Albert Einstein argued that under certain circumstances radiant energy itself seemed to consist of quanta (light quanta, later called photons), and in 1907 he showed the generality of the quantum hypothesis by using it to interpret the temperature dependence of the specific heats of solids. In October 1911 he was among the group of prominent physicists who attended the first Solvay conference in Brussels. The discussions there stimulated Henri Poincaré to provide a mathematical proof that Planck's radiation law necessarily required the introduction of quanta.

Planck was 42 years old in 1900 when he made the famous discovery that in 1918 won him the Nobel Prize for Physics and that brought him many other honours. It is not surprising that he subsequently made no discoveries of comparable importance. Nevertheless, he continued to contribute at a high level to various branches of optics, thermodynamics and statistical mechanics, physical chemistry, and other fields. He was also the first prominent physicist to champion Einstein's special theory of relativity (1905). “The velocity of light is to the Theory of Relativity,” Planck remarked, “as the elementary quantum of action is to the Quantum Theory; it is its absolute core.”

In his later years, Planck devoted more and more of his writings to philosophical, aesthetic, and religious questions. Planck believed that the physical universe is an objective entity existing independently of humans; the observer and the observed are not intimately coupled.

(b. July 7, 1861, Cavendish, Vt., U.S.—d. May 4, 1912, Baltimore, Md.)

A
merican biologist and geneticist Nettie Maria Stevens was one of the first scientists to find that sex is determined by a particular configuration of chromosomes.

Stevens's early life is somewhat obscure, although it is known that she taught school and attended the State Normal School (now Westfield State College) in Westfield, Massachusetts, in 1881–83. In 1896 she entered Stanford University, earning a B.A. in 1899 and an M.A. in 1900. She began doctoral studies in biology at Bryn Mawr College, which included a year of study (1901–02) at the Zoological Station in Naples, Italy, and at the Zoological Institute of the University of Würzburg, Germany. She received a Ph.D. from Bryn Mawr in 1903 and remained at the college as a research fellow in biology for a year, as reader in experimental morphology for another year, and as associate in experimental morphology from 1905 until her death.

Stevens's earliest field of research was the morphology and taxonomy of the ciliate protozoa; her first published paper, in 1901, had dealt with such a protozoan. She soon turned to cytology and the regenerative process. One of her major papers in that field was written in 1904 with zoologist and geneticist Thomas Hunt Morgan, who in 1933 would win the Nobel Prize for his work. Her investigations into regeneration led her to a study of differentiation in embryos and then to a study of chromosomes. In 1905, after experiments with the yellow mealworm (
Tenebrio molitor
), she published a paper in which she announced her finding that a particular combination of the chromosomes known as X and Y was responsible for the determination of the sex of an individual.

This discovery, also announced independently that year by Edmund Beecher Wilson of Columbia University,
not only ended the long-standing debate over whether sex was a matter of heredity or embryonic environmental influence but also was the first firm link between a heritable characteristic and a particular chromosome. Stevens continued her research on the chromosome makeup of various insects, discovering supernumerary chromosomes in certain insects and the paired state of chromosomes in flies and mosquitoes.

(b. Aug. 8, 1861, Whitby, Yorkshire, Eng.—d. Feb. 8, 1926, London)

B
ritish biologist William Bateson founded and named the science of genetics. His experiments provided evidence basic to the modern understanding of heredity. A dedicated evolutionist, he cited embryo studies to support his contention in 1885 that chordates evolved from primitive echinoderms, a view now widely accepted. In 1894 he published his conclusion (
Materials for the Study of Variation
) that evolution could not occur through a continuous variation of species, since distinct features often appeared or disappeared suddenly in plants and animals. Realizing that discontinuous variation could be understood only after something was known about the inheritance of traits, Bateson began work on the experimental breeding of plants and animals.

In 1900, he discovered an article, “Experiments with Plant Hybrids,” written by Gregor Mendel, an Austrian monk, 34 years earlier. The paper, found in the same year by Hugo de Vries, Carl Correns, and Erich Tschermak von Seysenegg, dealt with the appearance of certain features in successive generations of garden peas. Bateson noted that his breeding results were explained perfectly by Mendel's paper and that the monk had succinctly described the transmission of elements governing heritable traits in his plants.

Bateson translated Mendel's paper into English and during the next 10 years became Mendel's champion in England, corroborating his principles experimentally. He published, with Reginald Punnett, the results of a series of breeding experiments (1905–08) that not only extended Mendel's principles to animals (poultry) but showed also that certain features were consistently inherited together, apparently counter to Mendel's findings. This phenomenon, which came to be termed linkage, is now known to be the result of the occurrence of genes located in close proximity on the same chromosome. Bateson's experiments also demonstrated a dependence of certain characters on two or more genes. Unfortunately, he misinterpreted his results, refusing to accept the interpretation of linkage advanced by the geneticist Thomas Hunt Morgan. In fact, he opposed Morgan's entire chromosome theory, advocating his own vibratory theory of inheritance, founded on laws of force and motion, a concept that found little acceptance among other scientists.

Bateson later became the first British professor of genetics at the University of Cambridge (1908). He left this chair in 1910 to spend the rest of his life directing the John Innes Horticultural Institution at Merton, South London (later moved to Norwich), transforming it into a centre for genetic research. His books include
Mendel's Principles of Heredity
(1902, 2nd edition published in 1909) and
Problems of Genetics
(1913).

(b. May 15, 1859, Paris, France—d. April 19, 1906, Paris)

P
ierre Curie was a French physical chemist and cowinner of the Nobel Prize for Physics in 1903. He and his wife, Marie Curie, discovered radium and polonium in
their investigation of radioactivity. An exceptional physicist, he was one of the main founders of modern physics.

Educated by his father, a doctor, Pierre Curie developed a passion for mathematics at the age of 14 and showed a particular aptitude for spatial geometry, which later helped him in his work on crystallography. Matriculating at the age of 16 and obtaining his
licence ès sciences
at 18, he was taken on as laboratory assistant at the Sorbonne in 1878. There Curie carried out his first work on the calculation of the wavelength of heat waves. This was followed by very important studies on crystals, in which he was helped by his elder brother Jacques. The problem of the distribution of crystalline matter according to the laws of symmetry was to become one of his major preoccupations.

The Curie brothers associated the phenomenon of pyroelectricity with a change in the volume of the crystal in which it appears, and thus they arrived at the discovery of piezoelectricity. Later, Pierre was able to formulate the principle of symmetry, which states the impossibility of bringing about a specific physical process in an environment lacking a certain minimal dissymmetry characteristic of the process. Further, this dissymmetry cannot be found in the effect if it is not preexistent in the cause. He went on to define the symmetry of different physical phenomena.

Appointed supervisor (1882) at the School of Physics and Industrial Chemistry at Paris, Curie resumed his own research and, after a long study of buffered movements, managed to perfect the analytical balance by creating an aperiodic balance with direct reading of the last weights. Then he began his celebrated studies on magnetism. He undertook to write a doctoral thesis with the aim of discovering if there exist any transitions between the three types of magnetism: ferromagnetism, paramagnetism, and diamagnetism. In order to measure the magnetic
coefficients, he constructed a torsion balance that measured 0.01 mg, which, in a simplified version, is still used and called the magnetic balance of Curie and Chèneveau. He discovered that the magnetic coefficients of attraction of paramagnetic bodies vary in inverse proportion to the absolute temperature—Curie's Law. He then established an analogy between paramagnetic bodies and perfect gases and, as a result of this, between ferromagnetic bodies and condensed fluids. The totally different character of paramagnetism and diamagnetism demonstrated by Curie was later explained theoretically by Paul Langevin. In 1895 Curie defended his thesis on magnetism and obtained a doctorate of science.

In the spring of 1894, Curie met Marie Skłodowska. Their marriage (July 25, 1895) marked the beginning of a world-famous scientific achievement, beginning with the discovery (1898) of polonium and then of radium. The phenomenon of radioactivity, discovered in 1896 by Henri Becquerel, had attracted Marie Curie's attention. She and Pierre determined to study a mineral, pitchblende, the specific activity of which is superior to that of pure uranium. While working with Marie to extract pure substances from ores, an undertaking that really required industrial resources but that they achieved in relatively primitive conditions, Pierre himself concentrated on the physical study (including luminous and chemical effects) of the new radiations. Through the action of magnetic fields on the rays given out by the radium, he proved the existence of particles electrically positive, negative, and neutral; these Ernest Rutherford was afterward to call alpha, beta, and gamma rays. Pierre then studied these radiations by calorimetry and also observed the physiological effects of radium, thus opening the way to radium therapy.

Refusing a chair at the University of Geneva in order to continue his joint work with Marie, Pierre Curie was
appointed lecturer (1900) and professor (1904) at the Sorbonne. He was elected to the Academy of Sciences (1905), having received the Royal Society's Davy Medal jointly with Marie in 1903 and, jointly with her and Becquerel, the Nobel Prize for Physics. He was run over by a dray, which is a heavy cart used for hauling material, in the rue Dauphine in Paris in 1906 and died instantly. His complete works were published posthumously in 1908.

(b. Nov. 7, 1867, Warsaw, Poland, Russian Empire—d. July 4, 1934, near Sallanches, France)

P
olish-born French physicist Marie Curie (née Maria Skłodowska) was famous for her work on radioactivity. Curie was the first woman to win a Nobel Prize, and she is the only woman to win the award in two different fields. With Henri Becquerel and her husband, Pierre Curie, she was awarded the 1903 Nobel Prize for Physics. She was the sole winner of the 1911 Nobel Prize for Chemistry.

In 1891 Curie went to Paris and began to follow the lectures of Paul Appel, Gabriel Lippmann, and Edmond Bouty at the Sorbonne. There she met physicists who were already well known—Jean Perrin, Charles Maurain, and Aimé Cotton. She worked far into the night in her student-quarters garret and virtually lived on bread and butter and tea. She came first in the
licence
of physical sciences in 1893 and began to work in Lippmann's research laboratory. In 1894 she was placed second in the
licence
of mathematical sciences. It was in the spring of that year that she met Pierre Curie. They married the following year.

Following Henri Becquerel's discovery (1896) of a new phenomenon (which later was called “radioactivity”), Marie Curie, looking for a subject for a thesis, decided to
find out if the property discovered in uranium was to be found in other matter. She discovered that this was true for thorium at the same time as G.C. Schmidt. Turning her attention to minerals, she found her interest drawn to pitchblende, a mineral whose activity, superior to that of pure uranium, could be explained only by the presence in the ore of small quantities of an unknown substance of very high activity.