88 



and 



Mr. W. Crookes. [J ime 



where Tide denotes the number of portions of the path, per unit 

 distance in the direction inclined r + to a, which pass eitherwards 

 across the area in directions inclined to x at angles between the 

 values B-\A& and 6 + \de. The most general possible expression for 

 N is, according to Fourier, 



+ B! sin 20 + B 2 sin 40 + &c. 

 Hence the two members of (8) become respectively 



and 



........ (10). 



Remarking that A and A x are functions of aj, y, and taking 

 7 = cfody, we find, from (10), for the two totals of (7) respectively 



and i*JJvfody(Ao-i AO-v/IXE-V)] J 



where JfcM?/ denotes integration over the whole space enclosed 

 by (3). These quantities are equal if and only if JJ dxdyA l vanishes ; 

 it does so, clearly, if a = /3 ; but it seems improbable that, except 

 when = /3, it can vanish generally ; and unless it does so, our 

 present test case would disprove the Boltzmann-Maxwell general 

 doctrine. 



II. 4< On Electrical Evaporation." By WILLIAM CROOKES, F.R.S. 

 Received June 4, 1891. 



It is well known that when a vacuum tube is furnished with in- 

 ternal platinum electrodes, the adjacent glass, especially near the 

 negative pole, speedily becomes blackened, owing to the deposition 

 of metallic platinum. The passage of the induction current greatly 

 stimulates the motion of the residual gaseous molecules ; those con- 

 densed upon and in the immediate neighbourhood of the negative 

 pole are shot away at an immense speed in almost straight lines, the 

 speed varying with the degree of exhaustion and with the intensity 

 of the induced current. Platinum being used for the negative pole, 



