1868.] Mr. R. Moon on the Impact of Compressible Bodies. 



411 



It will be seen that the sodic sulphate and the magnesia sulphate also 

 occupy a place in Class I. 



V, Anhydrous salts examined in this memoir that do not form supersa- 

 turated solutions : — 



Potassic nitrate. 

 Potassic bichromate. 

 Sal-ammoniac. 

 Sodic nitrate. 

 Potassic chlorate. 

 Potassic ferrocyanide. 

 Baric nitrate. 

 Plumbic nitrate. 

 Ammonium nitrate. 



III. On the Impact of Compressible Bodies^ considered with re- 

 ference to the Theory of Pressure.'^ By B. Moon^ M.A., 

 Honorary Fellow of Queen's College, Cambridge. Communi- 

 cated by Prof. J. J. Sylvester. Beceived April 22, 1868. 



(Abstract.) 



Suppose that we have two rigid cylinders of equal dimensions, which have 

 their axes in the same straight line ; suppose, also, that one of the cylin- 

 ders is at rest while the other moves towards the first with the velocity V 

 in a direction parallel to both the axes ; the consequence of the colHsion 

 which under such circumstances must take place, will manifestly be that 

 half the momentum of the moving cylinder will be withdrawn from it, and 

 will be transferred to the cylinder which originally was at rest. 



The mode in which velocity or momentum will thus be collected from 

 the different parts of the one cylinder, and distributed amongst those of 

 the other, is obvious. Exactly the same amount will be withrawn from 

 the velocity of each particle of the impinging cylinder, and exactly the 

 same amount of velocity will be impressed on each particle of the cylinder 

 struck. 



And the reason of this is equally obvious ; since, if such were not the 

 case, the particles of each cylinder would contract — a supposition which is 

 forbidden by the very definition of rigidity. 



But if, instead of being perfectly rigid, each cylinder is in the slightest 

 degree compressible, a variation in the effect will occur. 



As before, momentum of finite amount will be transferred from the one 

 cylinder to the other, but the mode of collection of the velocity withdrawn 

 from the one, and the mode of distribution of that injected into the other^ 

 will no longer be the same as before. 



