﻿Notices respecting New Boohs. 149 



talking simple mathematical nonsense, and picturing to himself a 

 charged electric body or a magnetic pole from a fairly large 

 number (!) of points on whose surface emanate lines, which may 

 pretty well occupy the space immediately round the body, but 

 which diverge so much from each other at a short distance from it, 

 that space is there practically devoid of lines. The surface of the 

 body, thus conceived, strongly resembles the head of a pepper-caster, 

 while a much more accurate representation would liken it to the 

 surface of a golf ball. 



In the same way, another glaring absurdity is visited with just 

 severity (p. 109), — " The utterly vicious misuse of pressure to in- 

 dicate E.M.F. or voltage, by men who are old enough to know 

 better, and do." 



Some other terms put forward by Mr. Heaviside do not seem to 

 be so helpful. For example, the ratio of electric displacement to 

 electric force at auy point of a dielectric he proposes to call the 

 " permittivity " of the medium, because it indicates " the capacity 

 for permitting electric displacement." But a capacity for permit- 

 ting is no more identified with electric displacement than with 

 magnetic ; and hence there is nothing definitely suggestive in the 

 word. It can scarcely be doubted that " coefficient of electric 

 elasticity," as applied to its reciprocal, in accordance with usage in 

 the general theory of Elasticity, is a better term — and it is, in fact, 

 explicitly used by Maxwell, vol. i., art. 60 ; but, unfortunately, 

 Mr. Heaviside expressly rejects this helpful term, which does not 

 tax the memory, on the ground (see ' Papers,' Vol. II. p. 328) that 

 " the prefixing of adjectives is just one of those things that we 

 should try to avoid in a convenient terminology." On the con- 

 trary, I think, when the prefixing of an adjective secures clear and 

 proper definition, it should be adopted. 



The system of nomenclature is carried somewhat too far. We 

 do not want a name for every coefficient, and a wholly different 

 name for its reciprocal ; the list soon becomes too formidable ; 

 and it is a little amusing to find Mr. Heaviside, after telling us at 

 p. 21 that c in the equation D=cE is the " permittivity " of the 

 medium, telling us at the top of p. 24 that " c is the coefficient of 

 compliance, or the compliancy" — as if he thought that c still 

 required a little artistic touching. But " compliance " and " com- 

 pliancy " fail in helpfulness just as much as " permittance " and 

 " permittivity." The truth is that the problem to describe an 

 assigned quality of a body in a single, perfectly definite, and appro- 

 priate word no more admits of a solution than does at an arbitrary 

 moment in a game of Chess the corresponding problem to play 

 and mate in one move. 



Many people will, perhaps, think that in the word "forcive," for 

 a system of forces, conciseness is again a little overdone. 



It must be noted as worthy of commendation that Mr. Heaviside 

 systematically and in explicit terms always identifies the magnetic 

 induction at any point in a medium with a flux or displacement, and 

 thereby removes whatever obscurity is contained in Maxwell's 



