4 



Anniversary Address by Lord Rayleigh. [Nov. 30, 



drawn up a paper which has received the sanction of the Council and is 

 appended to this Address, and will, it is hoped, be of service at once to 

 authors and to the Society. (The paper is printed in Series A only.) 



Apart from questions of printing, the choice of symbols for representing 

 mathematical and physical quantities is of some importance, and is 

 embarrassed by varying usages, especially in different countries. A 

 Committee now sitting is concerned with the selection of symbols for 

 electrical and magnetic quantities, but the question is really much wider. 

 One hesitates to suggest another international conference, and perhaps 

 something could be done by discussion in scientific newspapers. Obviously 

 some give and take would be necessary. When the arguments from 

 convenience are about balanced, appeal might be made to the authority of 

 distinguished men, especially of those who were pioneers in the definition 

 and use of the quantity to be represented. As an example of the difficulties 

 to be faced, I may instance the important case of a symbol for refractive 

 index. In English writings the symbol is usually /t, and on the Continent n. 

 By the early optical writers it would seem that no particular symbol was 

 .appropriated. In 1815* Brewster has m, The earliest use of /j, that I have 

 come across is by Sir John Herschel,f and the same symbol was used 

 by Coddington (1829) and by Hamilton (1830), both distinguished workers 

 in optics. On the other hand, n was employed by Fraunhofer (1815), and 

 his authority must be reckoned very high. As regards convenience, I should 

 suppose that the balance of advantage would incline to /a, since n is wanted 

 so frequently in other senses. Another case in which there may be 

 difficulties in obtaining a much to be desired uniformity is the symbol for 

 electrical resistance. 



On a former occasion I indulged in comment upon the tendency of some 

 recent mathematics, which were doubtless understood as the mild grumbling 

 of an elderly man who does not like to see himself left too far behind. In 

 the same spirit I am inclined to complain of what seem unnecessary changes 

 in mathematical nomenclature. In my youth, by a natural extension of a 

 long established usage relative to equations, we spoke of the roots of a function, 

 meaning thereby those values of the argument which cause the function to 

 vanish. In many modern writings I read of the zeroes of a function in the 

 same sense. There may be reasons for this change ; but the new expression 

 seems to need precaution in its use ; otherwise we are led to such flowers of 

 speech as " zeroes with real part positive," which I recently came across.t 



* 'Phil. Trans.,' 1815. 



t ' Phil. Trans.,' 1821, p. 230. 



\ 1 Proc. Math. Soc.,' vol. 31, p. 266. 



