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XIX. Magnetic Qualities of Iron. 
By J. A. Ewing, M.A., F.B.S., Professor of Mechanism and Applied Mechanics in 
the University of Cambridge, and Miss Helen G. Klaassen, Lecturer in Physics, 
Newnham College. 
Received Jnne 7,—Read Jane 15, 1893. 
[Plates 34-41.] 
Recent applications of electricity, and especially the extended nse of transformers, 
have added particular interest to the study of cyclic magnetizing processes in iron. It 
has become a matter ol' consequence to investigate, in various specimens of metal, not 
only the amount of the energy dissipated by hysteresis in a magnetic cycle, but 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 sjDecific 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 i^oft iron was carried through a numerous series of cycles of magneti¬ 
zation, 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 ampli¬ 
tude 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 
* “Experimental Researches in Magnetism.’’ ‘ Phil. Trans.,’ Part II., 1885, p. 523. 
MDCCCXCIII.—A. 
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