The theory of two fluids 357 



The total repulsion between the two bodies is 



If we now put V 1 = A/\ ~ + ^S,^ + 1( 



o c 



the total repulsion becomes 



b + c b c 

 , 2 + S,S 2 -j- - 



The first term of this expression, with its sign reversed, represents the 

 attraction of gravitation, and the second term represents the observed electric 

 action, but the other terms represent forces of a kind which have not hitherto 

 been observed, and we must modify the theory so as to account for their non- 

 existence. 



One way of doing so is to suppose b = c and a^ = 2 = o. The result of this 

 hypothesis is to reduce the condition of saturation to that of the equality of 

 the two fluids in the body, leaving the amount of each quite undetermined. It 

 also fails to account for the observed action between the bodies themselves, 

 since there is no action between them and the electric fluids. 



The other way is to suppose that S 1 = S 2 = o, or that the sum of the 

 quantities of the two fluids in a body always remains the same as when the body 

 is saturated. This hypothesis is suggested by Priestley in his account of the 

 two-fluid theory, but it is not a dynamical hypothesis, because it does not give 

 a physical reason why the sum of these two quantities should be incapable of 

 alteration, however their difference is varied. 



The only dynamical hypothesis which appears to meet the case is to suppose 

 that the vitreous and resinous fluids are both incompressible, and that the 

 whole of space not occupied by matter is occupied by one or other of them. 

 In a state of saturation they are mixed in equal proportions. 



The two-fluid theory is thus considerably more difficult to reconcile with 

 the facts than the one-fluid theory. 



