ABSOLUTE ZERO

Evening Star, Issue 22456, 29 September 1936, Page 10

ABSOLUTE ZERO

APPROACH AT LEYDEN EXCITING VISTAS OPEN The low-temperature laboratory at Leyden University is a magnificent academic institution, writes the scientific correspondent of the. ‘ Manchester Guardian.’ As Leyden is a State university the laboratory is subsidised by the Hutch Government and the staff are Civil servants. It is named after Kamerlingh Onnes, who liquefied helium and discovered that some substances behave at very low temperatures as if they offered no resistance to electric currents. This discovery, like that of X-rays, was one of the great discoveries of physics, because it revealed the existence of an unsuspected state of matter. The phenomenon is still obscure, though F. and H. London, who have recently been working at Oxford, have published an interesting theory of it. They have suggested that the electric currents in supra-conducting substances, which apparently go on for ever when once started, are of a nature different from ordinary electric currents. They are to be conceived as resembling a magnetic rather than an electric phenomenon. Like a magnet, a supra-con-ducting circuit possesses its virtue for ever unless it is interfered with. The eminence of the Leyden laboratory is largely due to the far-sighted policy settled by Onnes. He included a school for instrument makers as an essential part of the organisation. The staff of this school are the chief mechanics to the research workers. As recognised 'teachers these mechanics have a higher status than laboratory mechanics elsewhere, and are not just workmen. This has had an important influence on the quality of work. The Leyden system has probably influenced the system of laboratory mechanics that has been organised in Soviet physic laboratories. There are about 90 ipupils in the school. Thus Leyden has a magnificent supply of technical assistants. This explains how the enormous number of exact measurements at low temperatures have been accomplished. The Dutch investigators have made the properties of many substances at temperatures near absolute zero as exactly known as the properties of ice and steam. They have aimed, at accumulating a wide range of data as a foundation for theory. The scientific research staff is restricted to four—W. H. Keesom, W. J. de Haas, E. C. Wiersma, and C. A. Crommelin. The administrative staff consists of one secretary and one typist. A large number of research students (from 30 to 50) can avail themselves of the technical resources. The subsidy for running the laboratory, which comes ultimately from the State, is about £3,000 a year (rather more than the running cost of the Cavendish Laboratory). This sura does not include upkeep of the building and salaries, but includes the cost of heating, gas, electricity, instruments, and materials used in the school. Special equipment, such as the big electro-magnet possessed by the laboratory, has been bought with special grants from the Rockefeller and other funds.

The most exciting recent experiment made at Leyden was the production by de Haas and Wiersma of a temperature of O.OOSdeg above absolute zero. As is generally known, heat is a mode of motion. The temperature of a body is measured by the speed of motion or vibration of its constituent particles. The temperature of a gas is determined by the average speed at which its molecules fly about. As the temperature decreases, the speed of the particles decreases. It is possible to calculate that the particles will lose all heat motion when reduced to a' temperature of about minus 273 deg. As the motions, and hence heat, have disappeared at that temperature it is impossibe to reach a lower temperature, so it is named the absolute zero. WHAT IT MEANS. Ordinary methods of stopping the heat motions of gases fail below temperatures of about O.Sdeg above absolute zero, because enormous pumping engines are necessary to obtain cooling by expansion of the gas. De H€as and Wiersma pushed, the limit down to O.OOSdeg by means of a trick based on an idea due to Langevin, Debye, and Giauque. These theorists explained that the arrangement of the molecules in a body absorbs a certain amount of energy. If the arrangement of the molecules could be suddenly changed at a very low temperature nearly all of the residual heat energy of the body might be absorbed in the rearrangement. In the experiments the rearrangement was made by means of a powerful field produced by the big electro-magnet. One of the substances used was chrome alum. It may be wondered why physicists are so excited by an approach from O.Sdeg to o.oosdeg of absolute zero. The importance is concealed by arithmetic; O.OOodeg is one-hundredth of O.Sdeg. Thus the extension of the low-temperature limit from O.Sdeg to O.OOSdeg is to be compared with an extension from the freezing point of water to 2.73 deg above absolute zero, or from Odeg C. to about minus 270 deg C. The study of bodies at temperatures from Odeg O. to minus 270 deg C., revealed a new region of phenomena. It is possible that the equivalent region between O.Sdeg and o.oosdeg absolute, and lower limits still, will also reveal unsuspected possibilities. Those who wonder about the practical value of the’search for absolute zero may reflect that through it eternal electric currents have already been discovered. It is conceivable that electrical engineering may ultimately be completely transformed by this discovery, as it might allow currents of enormous magnitude to be sent along conductors as thin as hairs, and perhaps allow the construction of powerful electrical machines in the space of a matchbox.