TO THE COMMITTEE OX ELECTRICAL STANDARDS. 197 



electric circuit is eijual to 1'2566 times the number of ampere- turns in 

 this circuit. 



3. That the termination -mice be used in general for words expressing 

 the pi'operties of a definite body or piece of matter ; e.g., resistance, con- 

 ductance, inductance, permeance, reluctance, &c. ; and that the termina- 

 tion -iriUj or -ility or the like be used for words expressing the specific 

 properties of a material ; e.c/., conductivity, resistivity, inductivity, refrac- 

 tivity, permeability, kc. 



The Committee recommend that they be reappointed ; that Professor 

 G. Carey Foster be Chairman and Mr. R. T. Glazebrook Secretary. 



APPENDIX. 



Magnetic Units. 



To the British Association Committee on Electrical Standards. 



Believing that the Committee is impressed with the convenience of 

 affixing names to some of the more important units connected with the 

 magnetic circuit, I beg to suggest the following considerations and 

 recommendations, which I will write out as briefly as possible. The state- 

 ments are intended to be precise in their terms ; but in several cases 

 alternative forms of definition are given. 



(1) That the unit coetEcient of self-induction, though frequently 

 useful, is by no means one of the most fundamental units, but should 

 be defined in a suitably subordinate manner, with reference to other and 

 more important quantities. 



(2) That it would be a mistake so to define it as to discourage the 

 employment of the same term for as many other quantities of the same 

 ' dimensions ' as possible ; especially for the unit coefficient of mutual 

 induction, and for unit 'permeance.' 



(3) That the essentially different quantities commonly called H and B 

 should be carefully kept distinct, although their measures in air have 

 been conventionally so arranged as to be numerically equal. 



[Summary of known facts and definitions.) — H being the intensity of 

 magnetic force at a point, or the slope of magnetic potential (w), 

 , i> 

 (J3 — oj,j := Hc^.y, along any length ab ; 



and in a closed magnetic circuit the circuitation of H is equal to 4:r times 

 the total electric current through the area bounded by the magnetic 

 circuit ; or, 



cycle \llds = circuitation of H = 4.TC<iS = -iTrC, 



or, at any point of space, 



curl H = VvH = i-c; 

 where c is current density. 



If the electiic circuit consists of n turns of wire threading the magnetic 

 circuit, and each conveying the current Cj, then C— «C,. 



