A New Field in Physics

-REVIEWSA NEW FIELD IN PHYSICS* FRANK ALLEN T HE development of the various branches of physical science has never proceeded from well-defined beginnings to deliberately chosen ends. At first it was impossible to discern either a beginning or an end. On the contrary, investigation progressed from commonplace observations to intimately related phenomena. Like Abraham of old, the primitive scientists went out not - knowing whither they went. In the last three centuries the desultory character of ancient scientific observation has indeed been superseded by a systematic search for the basic causes of natural phenomena. But the horizons of knowledge seemed continually to recede as investigation advanced, and while the new horizons were quite as alluring in their promise of finality, the promise once more proved illusive. One or two illustrations will make this point clear. The aggregations of matter in planets, sun, and stars, seemed ever to grow larger as more de:finite knowledge was secured, until some bodies forty times as massive as the sun have been located in the heavens. Even though there is some indication that stars have generally the same order of magnitude so far as their mass is concerned, it is always possible that among their countless numbers one may be found in which these apparent limits will be far exceeded. When in the contrary direction matter is subdivided, it is found to consist successively of minute *The Phenomenon of SupcrconductiDity, edited by E. F. Burton, University of Toronto Press, 1934. THE UNIVERSITY OF TORONTO QUARTERLY crystals, molecules, atoms, electrons, and protons, in a swiftly descending scale of smallness which irresistibly suggests Dean Swift's celebrated zoological epigram: So, Naturalists observe, a Flea Hath smaller Fleas that on him prey, And these have smaller still to bite 'em, And so proceed ad infinitum. In the less material sphere of undulatory motions, atmospheric and water waves, varying from a small fraction of an inch to many feet in length, are found, while the lengths of other waves employed in radiobroadcasting are measured in hundreds or thousands of yards, to which there is no necessary upper limit. In the opposite direction, ether waves of continually decreasing length are found in the infra-red heat r~diation, visible light, ultra-violet light, X-rays, and gamma rays, with apparently no limit of smallness. Similarly, temperatures are found ranging from hundreds of degrees to thousands or millions (and even to calculated temperatures for the interiors of stars of eighty millions of degrees) ·without discernible limit. But heat gives clear evidence of being a form of molecular energy, and, since relativity imposes a limit on the velocity of particles equal to the velocity of light, there must consequently exist an upper limit of temperature though its value does not seem to have been calculated. In all these cases the imagination is wearied in a futile attempt to discover some final limit upon which it may at last find rest. But when we turn to the scale of low temperatures, the theory of heat indicates a temperature at which the motions of molecules would cease and the last vestiges of temperature yanish. Experiment has shown the , absolute zero of temperature to be almost exactly 273 degrees below zero on the centigrade scale. 384 REVIEWS Below this absolute zero even the imagination cannot go. The absolute zero having been definitely calculated, efforts were soon made to reach it by the method of liquefaction of gases. The so-called permanent gases of the atmosphere for atime resisted all efforts to reduce them to a liquid condition. But in 1877, oxygen, nitrogen, and air were liquefied in the form of a transient mist, and a little later a small quantity of liquid oxygen was obtained. Since then, progress has been rapid, and low temperatures of- I8J° Centigrade for oxygen, -2.53° C. for hydrogen, and finally about -2.71° C. for helium, have been successively attained. In 192.6 it was theoretically shown that the sudden destruction of the magnetic condition in certain substances would lower their temperatures. Several of these materials were thereupon cooled in helium to 1.2.6 degrees above the absolute zero, and then, by suddenly destroying their magnetism, a...