The Becquerel Family

French physicists and chemists

• Alexandre-Edmond Becquerel
• Born: March 24, 1820
• Birthplace: Paris, France
• Died: May 11, 1891
• Place of death: Paris, France

• Antoine-César Becquerel
• Born: March 8, 1788
• Birthplace: Châtillon-Coligny, France
• Died: January 18, 1878
• Place of death: Paris, France

The remarkable Becquerel family spans four generations of science, with several of its members making important discoveries in physics and chemistry, particularly in the realms of electrochemistry, electromagnetic radiation, and radioactive decay physics.

Early Lives

Little is known of Antoine-César Becquerel’s (beh-krehl) early life. He is known to have served in the French army as an officer in the engineering corps until 1815. In 1837, he was appointed a professor at the Museum of National History in Paris, where he began work on numerous projects in physics and chemistry.

Alexandre-Edmond Becquerel was the second son of Antoine, the family’s founder. He did not attend a university but instead became assistant to his father at the Museum of Natural History at the age of eighteen. He later collaborated with his distinguished father on several important treatises. On the basis of his work, he received the doctor’s degree in 1840 from the University of Paris.

Antoine-Henri Becquerel spent his early years at the Lycée-Louis-le-Grand. Already showing his brilliance, in 1872 he entered l’École Polytechnique, transferring two years later to l’École des Ponts et Chaussées, where he would later work for ten years as chief engineer. From 1875 onward, he researched various aspects of optics and engineering, obtaining his doctorate in 1888. Appointed under his father at the museum, he became professor of physics there in 1892, gaining the chair both his father and grandfather had held. In 1895, he also earned the physics professorship at l’École Polytechnique, where he had started. In 1899, he was elected to the French Academy of Sciences, continuing in the family tradition.

Lives’ Work

Antoine spent his life at the Museum of Natural History in Paris. His works, during the early nineteenth century, were devoted to research on phosphorescence, fluorescence, thermoelectricity, the magnetic properties of materials, crystal optics, the theory of primary cells, and the electrical conductivity of matter. He is best known for his work in 1829, when he invented a primary cell with weak polarization.

After receiving his doctorate in 1840, Alexandre-Edmond became professor of physics at the Agronomy Institute of Versailles. While there, he became deeply involved in investigations of electricity and magnetism. His most significant discovery was the magnetic property of liquid oxygen. He was able to show that light, through the action of inducing chemical reactions, could cause the flow of an electric current. He invented an instrument that measured light intensity by determining the electric current intensity produced. As a by-product, he determined a means of measuring the heat radiated by objects hot enough to be emitting visible light by establishing the intensity of that light. He also originated the platinum-palladium thermocouple, which is used for high-temperature measurements.

Alexandre-Edmond’s interests became centered on fluorescence and phosphorescence phenomena. He was the first to discriminate between these ideas and used them for the study of ultraviolet and infrared radiation from 1857 to 1878. The problems where certain chemical materials absorbed light of one wavelength and then reemitted light of another wavelength fascinated him, particularly the circumstances in which substances were seen to glow in the dark. In 1859, he invented the phosphoroscope for doing detailed studies of light-emission intensity. As a side interest, he made the first complete solar spectrum photograph. His 1872 studies of the phosphorescence spectra or uranium compounds are considered the beginning of the path that led his son, Henri, to discover radioactivity.

Henri was involved, for most of his researches, with the phenomena of light. He had coauthored a series of memoirs with his father, Alexandre-Edmond, on the temperature of Earth, but his real interest was in light interactions in materials. Henri was the first physicist to observe rotatory magnetic polarization in gases. Expanding the experiment, he discovered the magnetic rotation of the plane of polarized light by Earth’s magnetic field. From 1886 to 1890, he performed experiments on the absorption of light by crystals, particularly investigating the anomalies of light passage along different axes within the crystal body. He then utilized that work to devise a new method of spectral analysis.

Fascinated by phosphorescence, Henri continued his father’s research. By determined and careful investigations, he discovered the laws relating to the emission of radiation by materials being bombarded by light waves. He also showed how the emitted phosphorescence decreased with time, and why it did so. The work for which Henri is best known involved his discovery in 1896 that uranium compounds emitted some type of invisible but highly penetrating radiation, a type of light wave that would contaminate photographic plates and greatly influence the electrical conductivity in gases. He had been researching the idea that fluorescing materials might be emitting X rays (which had recently been discovered by Wilhelm Conrad Röntgen).

With the aid of potassium uranyl sulfate, a fluorescent material, wrapped photographic negatives, and a fortuitous series of cloudy days, Henri discovered that the fogging of plates by the chemical did not depend on sunlight or phosphorescence but instead was a result of something’s being emitted by the compound itself. Ignoring the sun and the fluorescence process, he studied the radiation and showed that it was quite like X rays, particularly in causing air to ionize. The radiation was emitted continuously in an unending, uninterrupted stream, heading in all directions. At his suggestion, Madame Marie Curie undertook the study of those radiations for a large number of minerals. For a brief period, the radiation was called “Becquerel rays,” but in 1898, at Curie’s suggestion, the phenomenon was renamed “radioactivity.”

Henri’s observations were announced at the French Academy of Sciences meeting on February 24, 1896, in his article entitled “Émission de radiations nouvelles par l’uranium métallique.” He confirmed his studies with detailed work on the materials emitting the rays and on the properties of the rays themselves in “Sur diverses propriétés des rayons uraniques” (1896). By 1899, he had discovered that the radiation could be deflected by a magnetic field, so that at least some part of it had to be tiny charged particles: “Sur le rayonnement des corps radio-actifs” (1899). On the basis of further investigations, in 1900 he was able to announce that the part that was influenced by the field was negatively charged speeding electrons, identical to those identified in cathode-ray tubes by Sir Joseph John Thomson.

After identifying the uranium atoms as the radioactive portion of the compound in 1901, Henri concluded that the electrons radiated had to be coming from within the uranium atoms themselves. This was, in the physics world, the first real indication that the atom was not a featureless sphere, that it had an internal structure. For all of his illustrious work, but particularly for the discovery of radioactivity, Henri Becquerel was awarded, along with Pierre and Marie Curie, the 1903 Nobel Prize in Physics.

Members of the family continued achievements into the twentieth century. Henri’s son, Jean-Antoine-Édouard-Marie, also a member of the Paris Academy of Sciences, concentrated his work on the interactions of electromagnetic energy with solid materials. Notably, he studied the propagation of circularly polarized waves in various magnetic media. In addition, he did work on the anomalous dispersion of light by sodium vapors, the Zeeman effect in pleochroic crystals, and (with Heike Kamerlingh Onnes) the phenomena occurring in a substance placed in a magnetic field at the temperatures of liquid air and liquid hydrogen.

Significance

The Becquerels are outstanding examples of a family whose members distinguished themselves in science. Of its members, Alexandre-Edmond and Antoine-Henri played the grandest roles in the history of physics. Antoine-César, a pioneer in the development of electrochemistry, set a precedent by gaining the professorship of physics at the Paris Museum of Natural History—a position that was passed on through succeeding generations. Alexandre-Edmond’s discoveries on light, particularly its transmission in materials and its interactions with magnetic fields in minerals, laid the foundation for modern optical mineralogy and crystallography, vastly important in the fields of geophysical exploration and ore identification.

Alexandre-Edmond’s works, along with his father’s, on phosphorescence and fluorescence, paved the way for modern chemical studies on reaction rates, mechanisms, and complex formations. Henri, the best known of the family members, founded the field of radioactivity and furthered the use of light-magnetic-field interactions, particularly important in geology, optics, and electromagnetism. Moreover, his experiments helped to refute the belief, widely held during the late nineteenth century, that physics had produced all that it ever would. The idea of radioactivity, coupled with X rays, new elements, and quantum and relativity ideas, heralded the new age of modern physics.

Bibliography

Abro, A. d’. The Rise of the New Physics: Its Mathematical and Physical Theories. New York: Dover, 1951. This work covers all the major ideas and experiments that have led to modern quantum physics. Besides the topic of radioactivity, it deals with the people who worked with the Becquerels to extend the realms of physics. Contains chapters for readers with mathematical background, which can be skipped. Best suited for advanced students of physics.

Badash, Lawrence. “Marie Curie: In the Laboratory and on the Battlefield.” Physics Today 57, no. 7 (July, 2003): 37. Describes Becquerel’s experiments in radioactivity, and how Marie Curie continued his research to further the use of X rays.

Curie, Marie. Radioactive Substances. New York: Philosophical Library, 1961. This work deals with the research conducted by Marie Curie and her husband, Pierre Curie, based on Henri Becquerel’s discovery of radioactivity. Details their experiments, their hardships, and the discoveries they made. Tedious in spots, but presents a true picture of science at work.

Franklin, Allen. “The Road to the Neutrino.” Physics Today 53, no. 2 (February, 2003): 22. Information on experiments that scientists have conducted regarding the decay of beta rays, including Henri Becquerel’s discovery of radioactivity.

Holmyard, Eric. Makers of Chemistry. Oxford, England: Clarendon Press, 1931. A history of chemistry from its obscure beginnings to the modern science of the twentieth century. Details the explosion of chemistry programs in the nineteenth and twentieth centuries. Extensive pictures help describe important scientific contributions.

Ihde, Aaron. The Development of Modern Chemistry. New York: Harper & Row, 1964. This book covers the history of chemistry from ancient concepts of matter to present technology. Chapters on electrochemistry and radioactivity deal with the materials on which the Becquerels worked, including discoveries and interrelationships between physics and chemistry. Extensive references and pictures of the proponents of many theories.

Magie, William. A Source Book in Physics. New York: McGraw-Hill, 1935. This is a collection of the most important abstracts from physics in the last three centuries, from Galileo to Max Planck. Henri Becquerel’s discovery of radioactivity from uranium is presented, along with numerous articles on his predecessors. Allows the reader to see the high points of physics.

Ronan, Colin A. The Atlas of Scientific Discovery. New York: Crescent Books, 1983. Surveys the march of science, tracing the development of new fields of study and the new techniques they demanded. Excellent pictures; accurate and easy to read.

Taton, René. Science to the Twentieth Century. Vol. 4 in History of Science. New York: Basic Books, 1964. This work covers science from the Renaissance to the present, including astronomy, physics, chemistry, biology, and mathematics. All the major finds and their discoverers are included from Europe and North America. Numerous illustrations are provided, as are some asides on other areas of the world. Detailed and complicated reading.

Toulmin, Stephen, and June Goodfield. The Architecture of Matter. New York: Harper & Row, 1962. This reference work deals with the evolution of the scientific ideas of animate and inanimate matter in terms of chemistry and physics. Various theories of matter are presented to illustrate turning points and breakthroughs. Covers significant experiments and ideas through time. Good references and lively exposition.