298 Mr. R. H. M. Bosanquet on Electromagnets. 



which is more correct than the formula usually given hitherto 

 for the ratio of the shunt- and series-windings, and which 

 assumes absence of saturation terms. 



The simplicity of these results, no less than that of the pro- 

 cesses by which they are derived, lends additional value to the 

 new formula of Dr. Frolich, whose work deserves to be more 

 widely known and recognized than it now is. 



City and Guilds of London Technical College, 

 Finsbury, June 1886. 



XXXV. Electromagnets. — V. The Law of similar Electro- 

 magnets. Saturation, Sfc. By R. H. M. Bosanquet, 

 St. John's College, Oxford. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



IN previous papers on Electromagnets I have (1)* indicated 

 the general nature of a formula for the moment and in- 

 duction in electromagnets, and in subsequent papers f given 

 the details of the complete examination of the permeabilities 

 of many specimens of iron and steel, together with an attempt 

 at a molecular formula for these permeabilities worked out in 

 some detail. In the present communication I propose to give 

 as shortly as possible an abstract of the results of a great 

 number of experiments having special reference to the mag- 

 netic resistance of cylindrical bars of length equal to twenty 

 times their diameter, with and without pole-pieces. 



The datum in question (magnetic resistance) is that needed 

 to define the magnetism under given electromagnetic exci- 

 tation. 



The experiments cover the whole region from small mag- 

 netic inductions up to saturation, or what would be commonly 

 called so. 



The experiments have been made on bars of different sizes 

 of the proportions in question, so as to furnish for the first 

 time an experimental examination of the law of the magnetism 

 of similar solids. It appears to be of great interest to ascer- 

 tain how far this law can be depended upon in practice. 



The result is that, while in the main the law is conformed 

 to, the irregularity shown by different specimens, especially 

 in the extreme regions of small inductions and saturation, is 

 very great. General deductions therefore, such as have been 

 recently published, depending on the behaviour of single 



* Phil. Mag. xvii. p. 531. t Ibid. xix. pp. 73, 333; xx. p. 318. 



