Mr. J. C. Maxwell on the Dynamical Theory of Gases. 185 



mary coil, no metallic connexion for the primary current ; and yet 

 a notable effect was produced. 



I did not at the time publish this experiment further than by 

 communicating it to a few friends, hoping to be able to find a 

 satisfactory explanation of it. All I have observed since is that 

 the effect is dependent upon the condenser ; for when that is re- 

 moved no result is produced. 



It would appear, then, to depend on an electrical wave or im- 

 pulse shot, so to speak, into the uncompleted primary coil, similar 

 to the wave which will deflect in succession magnetic needles 

 placed at different distances on a telegraphic cable, without the 

 current passing through the whole length of wire, as shown in 

 the experiments of Mr. Latimer Clark and others. But why 

 there should be no effect, or an inappreciable one, when the pri- 

 mary circuit is completed, the current being alternated by the 

 rotation of the coils of the magneto-electric machine, I cannot 

 satisfactorily explain. 



XXII. On the Dynamical Theory of Gases. 

 By J. Clerk Maxwell, F.R.SS.L. $ E. 



[Concluded from p. 145.] 



On the Final Distribution of Velocity among the Molecules of Two 

 Systems acting on one another according to any Law of Force. 



FROM a given point let lines be drawn 

 representing in direction and magnitude 

 the velocities of every molecule of either kind 

 in unit of volume. The extremities of these 

 lines will be distributed over space in such a 

 way that if an element of volume dV be taken 

 anywhere, the number of such lines which 

 will terminate within dV will be f(r)dV, 

 where r is the distance of dV from 0. 



Let OA. = a be the velocity of a molecule of the first kind, and 

 OB — b that of a molecule of the second kind before they en- 

 counter one another, then BA will be the velocity of A relative 

 to B ; and if we divide AB in G inversely as the masses of the 

 molecules, and join 0G-, OG will be the velocity of the centre of 

 gravity of the two molecules. 



Now let OAW and 0B = # be the velocities of the two 

 molecules after the encounter, GA = GA' and GB = GB', and 

 A'GB' is a straight line not necessarily in the plane of OAB. 

 Also AGA' = 20 is the angle through which the relative velocity 

 is turned in the encounter in question. The relative motion of 



