Ampère had sought for some sort of mechanism for the transmission of electromagnetic currents. His own discoveries and those of Örsted led him to formulate the hypothesis that the field in the vicinity of a magnetic body is produced by a number of exceedingly small circular currents which flow undamped in or around the molecules and that magnetization consists merely of the bringing of these molecular currents into a parallel direction. But it was difficult for some physicists, even in Ampère’s day, to accept the hypothesis of undiminished currents _possessing no resistance_. If we transform the idea of the “molecular currents” of Ampère into the language of today, substituting for these molecular currents electrons revolving in atoms, it can be shown that the great French scientist was substantially correct in his assumptions. In 1915 Dr. Albert Einstein and W. J. de Haas astonished the world of physicists by showing experimentally—by means of a most ingenious apparatus—that the “molecular currents” or revolving electrons really exist. In 1919, Professor Kramerlingh-Onnes, at the University of Leyden, was able to produce what he called _imitations of ampere currents_—i. e., “undiminished currents producing no resistance.” It was demonstrated that the resistance of pure gold and pure platinum differ very little if at all from nil at low temperatures. But wires of these metals, of absolute purity, are difficult to obtain, so mercury was selected for the experiments. The resistance of the metal at the lowest attainable temperature of liquefied helium,-271.5° C., (at a pressure of 3 mm. of the mercury column), proved to be immeasurably small. The resistance down to a position shortly below 4.2° K. (Kelvin’s absolute scale) suddenly dropped from a measurable amount to a value practically nil. It was found that the induced current remained in a state of circulation, and that the decrease in the strength of the current amounted to less than 1 per cent per hour, from which it followed that the “time of relaxation” must amount to more than four days![13] At the absolute zero of temperature, it is supposed that the orbits of electrons in atoms are perfect circles, whatever their paths may be at measurable temperatures. This motion of the electrons remains when all heat has disappeared, since it is not this motion of the revolution of the electrons in their orbits that is associated with the energy of heat. Heat is _a mode of motion of the atoms themselves_, not of their contained electrons; though increase of heat doubtless results in an increase in the average orbital velocity of the electrons.