388 ILLUSTRATIONS OF THE DYNAMICAL THEORY OF GASES. 



The probability of not being struck by a particle of the other kind in the same 

 distance is 



e 



Therefore the probability of not being struck by any particle before reaching a 

 distance x is 



and if Z, be the mean distance for a particle of the first kind, 



\ = fasM + it 1 1 + V -( s*N t ...................... (12). 



t, "v v t 



Similarly, if Z, be the mean distance for a particle of the second kind, 



N, ........................ (13). 



, 



The mean density of the particles of the first kind is N l M l = p lt and that of 

 the second N t M i = p r If we put 



(15), 



a 



and ^ 



C 



PROP. XII. To find the pressure on unit of area of the side of the vessel 

 due to the impact of the particles upon it. 



Let N= number of particles in unit of volume; 

 3/= mass of each particle ; 

 v = velocity of each particle ; 

 I = mean path of each particle ; 



then the number of particles in unit of area of a stratum dz thick is 



Ndz ........................................ (17). 



The number of collisions of these particles in unit of time is 



Ndzj ...................................... (18). 



