90 Prof. F. Y. Edgeworth on the 



or a hurricane ; if heard from the third wire (d = 0'240 cm.), 

 it would mean 160 miles per hour, a speed * which fortunately 

 transcends our storm nomenclature. 



7. At the close of these experiments I put up a couple of 

 these anemometers in my yard, but I have not yet obtained 

 sufficient material for discussion. The means of registry is to 

 bring the sounding wire on the whirling arm into unison 

 with the exposed anemometer, and to let the former wire 

 make its registry on the chronograph (§2). 



Brown University, Providence, U.S.A. 



XI. The Asymmetrical Probability- Curve. 

 By Professor F. Y. Edgeworth, M.A., D. C.L.f 



THE Probability-Curve may be described as an approxi- 

 mation to the law of frequency which governs the set 

 of values assumed by a function of numerous independently 

 varying small quantities ; the function and the limits within 

 which the variables range being such that the function may 

 be regarded as approximately linear ; so that we have nearly 



Q = Qo + Qi'qi + 0,2 92 + &c + Q/ q n % ; 

 where Q is the compound quantity under consideration ; 

 9ij #2? & c - are the elementary quantities ; Q/ is what Q 

 becomes when we differentiate with respect to q x , and sub- 

 stitute zero for each of the variables q l9 q 2 , . . . ; Q/> Qz'y • • • 

 are similarly defined ; Q is what Q becomes when zero is 

 substituted in Q for each of the ^'s — an absolute term which 

 may usually be omitted. ' 



The symmetrical probability-curve is & first approximation 

 which is commonly written 



y = ——- e ~c2; 

 \7TC 



where x is the abscissa along which the values of Q are 



* There is a possible optical analogy to which I may allude in passing. 

 If in relation to speeds of the order of molecular velocities, the lumini- 

 ferous aether maybe considered as evidencing viscosity (following in the line 

 of a well-known hypothesis of Lord Kelvin), we might then expect a 

 molecule in its passage through aether to " sing " optically ; in other words, 

 we might expect the aether to awake resonant vibrations in the molecule, 

 in the way in which the transverse harmonic vibrations of a wire are 

 evoked (§ 1 et seq.) when the air-tone is the fundamental. 



t Read before the Royal Society, June 1, 1894. Communicated by 

 the Author ; in a revised and abridged form. 



% On this condition see the present writer's paper in the Philosophical 

 Magazine, Nov. 1892. 



