250 Mr Bryan, A siviple test case of [Nov, 26, 



black is due to the greater rapidity with which the eye perceives 

 red light than that with which it perceives blue. If however the 

 alternations of white and black succeed each other with sufficient 

 rapidity, the new impression of a white patch will be produced 

 before that of its predecessor has vanished, and there will be an 

 overlapping of impressions, and the sensation will be that of a 

 mixture of colours, or of a more or less neutral tint. This is in 

 accordance with the observation that if several circular bands, 

 each partly black and partly white in equal proportions, are on 

 the same disc, but in some of the bands the whole of the black 

 parts is in one patch, while in others it is divided up into several 

 patches, then, when the disc is rotated so that the band which 

 presents only two alternations at each revolution is seen coloured, 

 the bands which present a greater number of alternations are 

 seen of a neutral tint. Also if the rotation is rapid enough the 

 bands all appear of a neutral tint. 



So far as he could test the theory by his own eyes it appeared 

 to him that the residual impression, left when the light from a 

 white object was suddenly cut off, was at first green and faded 

 out through a more or less blue or slate colour. The object must 

 not however be so bright as to dazzle the eye, the duration and 

 colour of the residual impression might in that case be very 

 different. He could see the colours of the discs best in bright 

 diffuse daylight, and could see hardly any colour when the discs 

 were in direct sunshine. 



(2) A simple test case of Maxwell's Latu of Partition of 

 Energy. By G. H. Bryan, M.A., Peterhouse. 



1. By Maxwell's Law of Partition of Kinetic Energy is meant 

 the statement that, if the kinetic energy of a given system be 

 expressed as a sum of squares, the mean values of these several 

 squares taken over a large number of systems distributed accord- 

 ing to a certain permanent or stationary law are equal. 



The following illustration will, I think, show very clearly, or 

 at any rate will throw some light on, how far this law is (i) a 

 possible, (ii) a necessary law, when the systems considered do or 

 do not collide with one another. 



2. Consider a rigid body moveable about a fixed point or 

 about its centre of gravity and acted on by no forces. The equa- 

 tions of motion are 



A^-{B-C)co,co, = 0,&c (1), 



