XIX. Magnetic qualities of iron

Abstract

Recent applications of electricity, and especially the extended use of transformers, have added particular interest to the study of cyclic magnetizing processes in iron. It has become a matter of consequence to investigate, in various specimens of metal, not only the amount of the energy dissipated by hysteresis in a magnetic cycle, hut the relative amounts under various degrees of magnetization and various intensities of magnetizing force. Other questions arise with regard to the dependence of this loss on the frequency of the cyclic process and on the manner in which it is performed. The experiments to be described in this paper deal mainly with the effects of cyclic variations of magnetizing force. They are intended to contribute some additions to existing data, to answer one or two specific questions, and to exemplify certain more or less novel methods of experimental inquiry. A section at the end of the paper relates to the molecular theory of magnetization, and its adequacy to explain some characteristic manifestations of magnetic hysteresis. Experiments on Rings, by the Ballistic Method. In a paper published eight years ago by one of us, experiments were described in which a piece of soft iron was carried through a numerous series of cycles of magneti­sation, of graded amplitude, with the object of determining the form taken by the curve of magnetization and magnetizing force during the process of reversal between any assigned limits, and of comparing the work spent in the process with the ampli­tude of the magnetization. A similar experiment was described for steel. Since then the importance of such information has been recognized by electrical engineers, and some experiments with a similar object have been made by Messrs, Evershed and Vignoles, and by Mr. C. P. Steinmetz. Notwithstanding, however, the increased interest which now attaches to the matter in consequence of its practical bearing, the available data are still meagre. By way of adding to them, we have made a detailed examination of some ten samples of wire and sheet iron, arranged in the form of rings to be operated on by the ballistic, method.