40 PROFESSOR KELLAND, ON MOLECULAR EQUILIBRIUM. 



former laminae is greater, and the part of the body on which it acts 

 less, we cannot have erred much in taking the mean as the correct 

 value of the attraction. 



Indeed, if there be any error committed, it is obvious that we have 

 estimated the attraction too high ; both from the greater density being 

 that which we have supposed to have full agency, and from the fact, 

 that the actual attraction on parts lying at a distance from the centre, 

 is not in the direction of the line joining the centres of the particles. 

 It may then be conceived, that the above expression is rather too great 

 for the attraction, and it will appear presently that its value even as 

 I have given it, is negative. 



iirPB 



For we have already proved (14) that , — = M; 



.-. — , — (\+al)e- al —J? = M (17); 



a o 



hence 



s = — 7^r~ (1 + aa) e " ~^~ e t ° * (1 + aa)t 



an essentially negative result. 



21. We may however introduce a positive quantity into this ex- 

 pression, by conceiving each molecule as a compound one of two 

 different kinds of particles attracting each other, as we proceed to 

 shew. 



M' 

 Let U'=^~, 



then the action on a particle of caloric is 



, (dU dU' dV 



P -T— + 



dx dx dx 

 hence all the equations for motion are unaffected : 



and Z> = 2 — „ — + 2 — ~ — , 



|S Ae~« R 1? A'e- aR '\ 4ttP 

 V ~ * \R ~ B + B " ' R ) « 8 ; 



