400 ILLUSTRATIONS OF THE DYNAMICAL THEORY OF GASES. 



whence the rate of diffusion due to the motion of translation may be found ; for 



<?, = ^, and <?,= -^ ......................... (45). 



"i "i 



To find the diffusion due to the motion of agitation, we must find the 

 value of q t . 



L d 



v, dx 



Similarly, ?,= + {l +ATr, (ft+jv)} .................. (47). 



The whole diffusions are <?, + <?! and Q t + q v The values of q t and q t have a 



term not following Graham's law of the square roots of the specific gravities, 



but following the law of equal volumes. The closer the material of the plug, 

 the less will this term affect the result. 



Our assumptions that the porous plug acts like a system of fixed particles, 

 and that Graham's law is fulfilled more accurately the more compact the 

 material of the plug, are scarcely sufficiently well verified for the foundation of 

 a theory of gases ; and even if we admit the original assumption that they are 

 systems of moving elastic particles, we have not very good evidence as yet for 

 the relation among the quantities A, B, C, and D. 



PROP. XX. To find the rate of diffusion between two vessels connected by a 

 tube. 



When diffusion takes place through a large opening, such as a tube con- 

 necting two vessels, the question is simplified by the absence of the porous 

 diffusion plug; and since the pressure is constant throughout the apparatus, the 

 volumes of the two gases passing opposite ways through the tube at the same 

 time must be equal Now the quantity of gas which passes through the tube 

 is due partly to the motion of agitation as in Prop. XIV., and partly to the, 

 mean motion of translation as in Prop. XV. 



