KAMERLINGH ONNES, HEIKE (1853–1926)

Heike Kamerlingh Onnes was born on September 21, 1853, in Groningen, the Netherlands, and died on February 21, 1926, in Leiden. His father owned a roof-tile factory. Heike Kamerlingh Onnes entered the University of Groningen to study physics. When the government threatened to permanently shut down the university for monetary reasons, he led a delegation to the seat of the government in the Hague as president of the student government. During his studies he won several prizes in physics; his Ph.D. thesis demonstrates superior mathematical abilities. Despite delicate health through much of his life, he showed an enormous capacity for work.

Kamerlingh Onnes does not fit the description of a loner; on the contrary, he created one of the first laboratories to be set up as if it were a factory. Per Dahl in his comparison between Kamerlingh Onnes and his British counterpart, James Dewar, states that Onnes, to be sure was paternalistic, opinionated, and a man of strong principles—traits not uncommon among the moguls of late nineteenth-century science—but that he proved to be a benevolent leader, kind and scrupulously fair in his relations with friends and pupils alike—behavior that was certainly within the norms of his time.

After Kamerlingh Onnes was appointed professor in experimental physics at the University of Leiden in 1882, he stated in his inaugural lecture that physics is capable of improving the well-being of society and proclaimed that this should be accomplished primarily through quantitative measurements. He laid out what he was going to do and, to the surprise of onlookers, that is what he did. He was an excellent organizer, and set out to equip his laboratory on a grand scale. The city of Leiden did not yet provide electricity, so he acquired a gas motor and generator and made his own electricity. Pumps and compressors were barely available, so he had them made in the machine shops of the laboratory. There was a need for measuring instruments, so he created an instrument makers' school. There was an even greater demand for glassware (Dewars, McLeod gauges and connecting tubes, etc.), so he created a glassblowers' school that became famous in its own right.

All currents that had to be measured were sent to a central "measurement room" in which many mirror galvanometers were situated on top of vibration-free columns that were separated from the foundations of the building. One should realize that the many announcements in the early literature of the liquefaction of specific gases pertained to not much more than a mist or a few drops; Kamerlingh Onnes planned to make liquid gases by the gallon. A separate hydrogen liquefaction plant was located in a special room with a roof that could be blown off easily.

The availability of large quantities of liquid helium as well as an excellent support staff led to the undertaking of many experiments at 8 K (the boiling temperature of helium) as well as the lower temperatures obtained by pumping. One subset was the measurement of the resistivity (conductivity) of metals, since this property was useful as a secondary thermometer. Although a linear decline was observed, various speculations were made as to what the result would be when zero absolute temperature was reached. In April 1911 came the surprising discovery that the resistivity in mercury disappeared. At first the surprise was a sharp jump to what was thought to be a small value. The first reaction to this baffling result was to suspect a measurement error. All electrical machines in the laboratory were shut down to be sure that there were no unforeseen current leaks and the experiment was repeated several times. Very careful verifications finally showed that the effect was real and that the resistance was indeed unmeasurably small ("sinks below 10^-4 of the resistance at 0°C"), and moreover it was found that the effect existed also in other metals, even those that could not be purified as well as mercury.

Initially there was speculation about building an "iron-less" magnet, but this hope was dashed when it was discovered that a small field destroyed the superconductivity. Not until 1960 when materials where found that could sustain high fields, did superconductivity show promise for building strong magnets. The other obstacle was the need for a low-temperature environment. Raising the critical temperature had been a goal for many years, and a spectacular breakthrough was made in 1986.

The result was called by Dutch physicist H. A. Lorentz "perhaps the most beautiful pearl of all [of Kamerlingh Onnes's discoveries]." However, as H. B. G. Casimir describes in his memoirs, he refused to give any credit to the graduate student who observed the phenomenon and who realized its importance.

Although the discovery can be called accidental, one may ask what led up to it. The decline in resistivity of metals when the temperature was lowered clearly invited further study. This program (J. van den Handel calls it Kamerlingh Onnes's second major field of research; liquefaction being the first) was both intrinsically interesting as well as relevant to the construction of a good secondary thermometer. It was known that the resistivity was a linear function of the temperature but was noticed to level off at lower temperatures. The height of this plateau was found to depend on the amount of impurities, using a series of experiments with gold, since the amount of admixture in this metal can be easily controlled. To lower this plateau, a metal of very high purity was needed. Since zone melting, in the modern sense, did not exist, the choice fell on mercury, because this metal could be purified by distillation, and the purified liquid was then placed in glass capillaries. When the liquid in these capillaries was frozen, it formed a "wire." Moreover, it became clear that these wires were free of dislocations, to use a modern term, because it was found that pulling of the wires resulted in increased values of the residual resistance. Hence mercury was the best bet to see how far the linear part of the resistivity curve could be extended to lower temperatures. The hope to have a linear resistor at very low temperatures was certainly a driving factor for the research that led to the discovery of superconductivity.

Heike Kamerlingh Onnes was awarded the Nobel Prize in physics in 1913.

Paul H. E. Meijer

See also: Electricity; Energy Intensity Trends; Heat and Heating; Heat Transfer; Magnetism and Magnets; Molecular Energy; Refrigerators and Freezers; Thermal Energy.

BIBLIOGRAPHY

Bruyn Ouboter, R. de. (1997). "Heike Kamerlingh Onnes's Discovery of Superconductivity." Scientific American 276:98–103.

Casimir, H. B. G. (1983). Haphazard Reality: Half a Century of Science. New York: Harper and Row.

Dahl, P. F. (1992). Superconductivity: Its Historical Roots and Development from Mercury to the Ceramic Oxides. New York: American Institute of Physics.

Handel, J. van den. (1973). "Kamerlingh Onnes, Heike." In Dictionary of Scientific Biography, Vol. 7, ed. C.C. Gillispie. New York: Charles Scribner's Sons.

Meijer, P. H. E. (1994). "Kamerlingh Onnes and the Discovery of Superconductivity." American Journal of Physics 62:1105–1108.

Nobel, J. de. (1996). "The Discovery of Superconductivity." Physics Today 49(9):40–42.