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January 28th, 1840. 

 JOHN ANSTER, LL.D., Vice-President, in the Chair. 



Professor Jellett read the following Abstract of a Paper 

 on the Equilibrium or Motion of a Molecular System. 



The object of the present paper is to deduce, on the most 

 general theory of molecular action, the equations of equili- 

 brium or motion of a body, solid or fluid, whose several par- 

 ticles have been displaced from their position of equilibrium. 



The action of any one particle or molecule of a body upon 

 another will in general depend on the state of the two mole- 

 cules, on their primitive positions, and on their displaced po- 

 sitions. If it be supposed that the state of a particle, that is 

 to say, its capacity of exerting force, is not altered by the dis- 

 placement of the surrounding particles, it is plain that the 

 force developed by the displacement of two molecules will be 

 of the form 



f{x, y, z, x, y, z, ^, ^, ^, ^', ^', ^',), 



where x, y, z are the co-ordinates, and ?, rj, Z, the resolved 

 displacements of the first particle ; x, y, z', |', -q, Xi, having 

 the same signification for the second. The hypothesis here 

 made may be termed the hypothesis of independent action. 



Adopting this hypothesis, and modifying the foregoing 

 expression by the observation that no molecular force is deve- 

 loped by a mere translation of the entire system from one po- 

 sition to another, the value of the force will be 



Fo + A(^'-K) + B {n -ri)+C{K'- l\ 

 Fq, a, B, C being of the form 



f{x,y, z, x\y', z'), 

 or 



/(«, y, z, p, 6, <p), 



