Mr. K. H. M. Bosanquet on Electromagnets, 339 



These will be applied to the law first obtained. A discussion 

 of the actual behaviour of my Gramme dynamo will follow in 

 a future paper. 



The average values of the magnetic resistance of a number 

 of bars with pole-pieces throughout the whole course of 

 magnetization were given in the investigation above cited. 

 The bars in question all had cores of the same shape, viz. 

 length : diameter : : 20 : 1. The numbers for other shapes will 

 no doubt be different, and the laws which deal with the shapes 

 will be the subject of future investigation; but it is not likely 

 that the general type of the law will differ materially from 

 that here discussed. 



It has been a matter for some consideration what scheme 

 should be adopted for the representation and comparison of 

 the different laws. I have adopted a scheme in which the 

 magnetic inductions are measured horizontally, and the 

 permeabilities, or, as I prefer to call them, conductivities, 

 vertically. 



The reason for adopting the magnetic induction as the 

 chief variable, is the fact that the magnetic properties of the 

 metal depend only on the induction. It is enough to glance 

 at the figures which follow, or, better, at the reciprocal figures 

 representing magnetic resistance at p. 303 of the paper above 

 cited, to see that, whether the metal be in the form of rings, 

 or of bars with or without pole-pieces, the resistance to 

 magnetization (or its reciprocal the conductivity) changes 

 always in much the same way at the same values of the 

 induction. Any representation which overlooks this, overlooks 

 the principal law so far known as to the variation of the 

 magnetic properties of iron. And I dissent from the position 

 of those who say that the magnetizing current, or magneti- 

 zing force, has the chief claim to be regarded as the 

 independent variable in such a representation. 



I have in this case chosen conductivity, rather than the 

 magnetic resistance, to be combined with the magnetic 

 induction, mainly because this combination represents Fro- 

 lich's law, which is so generally accepted, as a straight line ; 

 and this facilitates the comparison of Frolich's law with other 

 laws. 



A few words as to the precise meaning of the expressions 

 permeability and conductivity. 



The word permeability was originally used in connection 

 with the old theory, and was the ratio 



13 magnetic induction 



«£) magnetizing force ' 



2A2 



