Charles-Édouard Guillaume

Swiss physicist

• Born: February 15, 1861
• Birthplace: Fleurier, Switzerland
• Died: June 13, 1938
• Place of death: Sèvres, France

Measurements, and the standards on which they are based, are the foundation of the physical sciences. Guillaume, during his long tenure as assistant director and director of the International Bureau of Weights and Measures at Sèvres, was indefatigable as researcher and administrator in refining instruments and methods of measurement to the greatest possible precision, and in publishing to the world the current status of metricization and metric standards. For his efforts, he received the Nobel Prize in Physics in 1920.

Early Life

Charles-Édouard Guillaume (shawrl ay-dwahr gee-yohm) was born in Fleurier, in the canton of Neuchâtel in western Switzerland, about eighty-five kilometers from Geneva. His father and grandfather were watch and clock makers. Guillaume attended the local schools, then the gymnasium in Neuchâtel, and entered the Technical University in Zurich at the age of seventeen. He received his doctorate five years later, in 1883, with a thesis on electrolytic capacitors. In the same year, after a few months as an artillery officer, he entered the International Bureau of Weights and Measures at Sèvres, France, where he would spend his entire scientific career (retaining his Swiss citizenship until his death).

The first task that the bureau gave him was the study of the mercury-in-glass thermometer, its calibration and its stem correction (the correction necessary when the thermometer is only partially immersed in the medium whose temperature is to be measured). This innocuous-sounding assignment resulted in the ninety-two-page Études thermométriques (1886; studies in thermometry), later expanded as the Traité pratique de la thermométrie de précision (1889; practical manual of precision thermometry), which became the standard textbook in the field. During these early years in the bureau, Guillaume met and married A. M. Taufflieb; they had three children.

Another early research by Guillaume upset one of the defining standards of the metric system. The kilogram was originally declared to be the mass of one cubic decimeter (one thousand cubic centimeters) of water at its temperature of greatest density, 4 degrees Celsius. Guillaume determined that a kilogram of water at this temperature in fact occupies 1,000.028 cubic centimeters, a finding that caused physical scientists thereafter to express volumes in milliliters, leaving the cubic centimeter to their less exacting medical colleagues. The units were declared equal in 1964, but the distinction persists.

Life’s Work

The research that occupied more than three decades of Guillaume’s life, for which he was specifically awarded the Nobel Prize, began as a fairly straightforward activity of the International Bureau of Weights and Measures. In 1889, the bureau decided to distribute prototype standards of length and weight to the nations of the world that subscribed to the metric system. The platinum-iridium standards used by the bureau were too expensive for wholesale replication, and by 1891 Guillaume hit on pure nickel as a relatively cheap, noncorrosive, and machinable metal for meter and kilogram prototypes. Thus, the distribution of the standards to the bureaus of standards in various countries was solved, and laboratory and industrial measurements could be referred to the local standards without the inconvenience of crossing oceans or international boundaries.

However, one important type of measure was overlooked: geodesy, or the precision measurement of land areas, distances, and directions. Geodesy standards at the turn of the century were clumsy, four-meter bars with scribed lines at each end, aligned by microscope, and protected in the field from weather and temperature changes (which changed the bars’ lengths) by portable huts. The baselines measured with these bars could be kilometers long, and the measuring teams numbered as many as sixty skilled workers, who could work for days at a single baseline. For simplicity and decreased expense, new methods were obviously needed.

New methods developed, in Guillaume’s hands, from new materials. For manufacturing reasons, the nickel of the smaller standards could not be used in the long rods of geodetic measurement. Other materials were required. In 1895, Guillaume began the study of nickel-iron alloys, or nickel steels, with nickel content of 25 percent and above. Long and painstaking studies (literally thousands of alloy bars and rods were tested) showed that nickel steels containing 35.8 percent nickel exhibited a thermal expansivity (change of length with temperature) less than one tenth that of nickel or iron by itself. Moreover, treatment in finishing the nickel steel (forging and controlled-temperature cooling) could reduce temperature expansivity to almost zero. The alloy of this composition was given the name “invar,” because of the invariability of its length with changes in temperature. Invar’s application in geodesy was quickly found. Guillaume produced a twenty-four-meter invar wire for E. Jäderin, leader of the Spitzbergen (surveying) Expedition of 1899-1900, which could be carried in a coil and used without temperature precautions or microscopic alignment. Jäderin reported measurement of a baseline more than ten kilometers long with an error of less than nineteen millimeters. In subsequent years, geodetic measuring devices converted completely to invar.

Measurement of time also yielded to invar. Pendulum chronometers were the standard of the day. The period of a pendulum is dependent on its length, and ordinary metals such as brass or steel change length with temperature, requiring that precision instruments be kept in a temperature-controlled environment. Pendulum arms made of invar freed these devices from that requirement and took time measurement out of the laboratory and into factories and government offices.

Uses for invar were also found outside measurements and standards. Railway switches at the time were operated by hand levers in a switch tower that was sometimes hundreds of meters from the switches themselves. The connecting cables could contract enough in very cold weather to throw a switch, or slacken enough in heat to make the switch inoperable. The use of invar cables eliminated this problem.

If invar could be made with zero temperature expansion, nickel steels of slightly different composition could be made with any desired expansivity specifically, that of glass. Light bulbs of the time were made with their electrical leads sealed into glass bases, requiring that the metal of the leads have the same temperature-expansion behavior as glass to preserve a gas-tight seal. The only metal that possessed this property was platinum. Mass commercial application of electric light was impossible with expensive platinum, but a nickel steel of the required expansivity was developed and made light bulbs available to all.

Nickel steels in the range of 25 percent to 35 percent nickel also show interesting magnetic anomalies: At low temperatures, they are magnetic, but above a certain temperature they are nonmagnetic. Below this transition temperature, they are again magnetic. This finding led to the construction of thermostats based on magnetic coils. These were fixed-temperature devices, not variable like house thermostats, because the percentage of nickel was fixed; yet any given temperature could be chosen initially, because the transition temperature varied with the nickel content.

In the course of developing invar, Guillaume evaluated ternary alloys and discovered one, containing about 12 percent chromium in addition to the iron and nickel, that showed zero (or even negative) change in elasticity with temperature change. This combination was named “elinvar,” and it completed the revolution in horology and chronometry that had begun with the invar pendulum. The accuracy of chronometers depends on the constancy of size of pendulum, balance wheel, and other parts, but also on the constancy of elasticity of the hairspring mechanisms of the balance wheel. The designs of the time used complex pairings of metals (mostly steel and brass), whose changes in length and elasticity offset each other so long as temperature changes were not too great. Elinvar at one stroke eliminated the need for this kind of design and brought chronometry to the peak of mechanical perfection that yielded, finally, only to electronic measurement. Elinvar was so successful and inexpensive, in fact, that within a very few years mass-produced watches used nothing else for hairsprings.

In all of these researches on alloys, it was Guillaume, the standards-of-measurement person, who directed Guillaume, the metallurgical investigator. Standards of the time were material and mechanical bars with scribed lines, carefully adjusted masses of metal, carefully adjusted physical volumes, and the like. Modern standards are determined by optical and electronic methods length and time through wavelengths and frequencies of light, for example. At the turn of the century, however, improvements in standards had to come not from improvements in circuitry but from improvements in methods and materials.

Significance

Guillaume knew exactly what he wanted his materials to do, and exactly how to apply the properties of those materials when he found what he wanted. This is the story behind the discovery of invar and elinvar and not merely a happy accident that turned out to have useful consequences. Guillaume’s was a determined search for exactly the right materials for the task at hand measurement. Guillaume reported his findings in more than half a dozen book-length publications from 1897 to 1927, as well as in numerous papers in research journals.

The final reason for Guillaume’s importance in science was his determination to communicate not only his own research but also the status of metric research and the metric system worldwide to the scientific community and all interested laypersons. His earliest work in this line, Unités et étalons (units and measures), appeared in 1893, when he was still a staff member of the bureau. Other works appeared when he was assistant director and director, including the series of biennial reports, Les Récents Progrès du système métrique (recent advances in the metric system), that were published from 1907 through 1933, many as books. Guillaume took his position as director of the bureau seriously and tirelessly propagandized, in the best sense of the word, for the metric system. To those who knew his work, he represented the International Bureau of Weights and Measures and the metric system. He continued in this position until he retired as director in 1936. Even as honorary director, he remained active until he died on June 13, 1938.

Bibliography

Chaudron, Georges. “Charles-Édouard Guillaume.” In Dictionary of Scientific Biography, edited by Charles Coulston Gillispie, vol. 5. New York: Charles Scribner’s Sons, 1981. A rare biographical treatment of Guillaume that includes a bibliography of his works.

Guillaume, Charles-Édouard. Interview in Scientific American Monthly 3 (February, 1921): 105-109. This article describes the activities of the International Bureau of Weights and Measures. Includes photographs and Guillaume’s own work.

“Obituary: Dr. C.-E. Guillaume.” Nature 142 (August 20, 1938): 322-323. Gives a brief biographical account and discusses Guillaume’s scientific achievements.