208 REPORT— 1895. 



As regards the magnitude of the unit of inductance. While I agree with 

 Mr. Heaviside and Dr. Lodge that the unit pole ought to have been so 

 defined that the mutual force between two poles is equal to their product 

 divided by the surface of a sphere whose radius is their distance, a defini- 

 tion which would have made the line-integral of H due to a current C 

 equal to C itself instead of to 477C, I deprecate a mixing up of the two 

 systems. So long as we employ our present unit of intensity of mag- 

 netic field, which results from our present definition of the unit pole, we 

 cannot consistently reckon the line integral as equal to the ampere-turns. 

 It must be reckoned as iir times the ampere-turns, and the flux N must 

 be reckoned as 4-/t times the ampere-turns. The practical inconvenience 

 of retaining the factor in- cannot be considerable, for it is as easy to tabu- 

 late the values of 47r/i as the values of fx. 



Next as regards ' permeance.' I do not think it can conveniently be 

 I'eckoned in henrys. I would rather reckon it in ' webers per ampere- 

 turn,' which would be written ' web. per amptu ' ; and there can be no 

 possible doubt as to the meaning intended when once we have fixed the 

 magnitude of the 'weber.' There seems to be no diflerence of opinion a 



to what this magnitude should be. It is fixed by the relation E =-~j-, 



E being in volts, N in webers, and t in seconds. This is in accordance 

 with Dr. Lodge's proposal ; but Dr. Lodge has not explicitly recommended 

 any name for the physical quantity which is measured in webers. Shall 

 we call it ' weberage ' ? It greatly needs a name ; for ' induction ' may 

 mean B instead of the surface integral of B, besides having many other 

 meanings. 



When permeance varies according to the strength of current, I would dis- 

 tinguish between 'total permeance' ^ and 'differential permeance' ^ ^,- 

 ° ^ nC ndC 



As regards ' gaussage ' and ' gauss f al I think the names will be 

 convenient in the senses proposed by Dr. Lodge, but I cannot agree with 

 his selection of a unit of measurement. The present definition of the 

 unit pole (on which the present unit current is based) requires us to 

 equate the line-integral in question to 47r7iC. 



To be consistent we must reckon gaussage as equal to iir times the 

 number of amptus. Dr. Lodge's proposal is to reckon C, not in amperes 

 but in c.g.s. units, thus introducing, as it appears to me, an awkward 

 breach of continuity. j j^ Everett. 



Professor Carey Foster has written objecting to the term ' gauss- 

 gradient,' instead of ' magnetic gradient ' ; he prefers the latter, just as he 

 would prefer 'temperature-gradient' to 'degree-gradient.' 



Dr. Johnstone Stoney has also written, urging strongly that not the 

 c.g.s. unit of magnetic potential, but one-tenth of this quantity, should 

 receive a name, in order to make it harmonise with the ampere series ; 

 and further recommending that the names ' weber ' and ' gauss,' as above 

 suggested, should be interchanged. 



