290 M. Avogadro on the relation of' the Density of Bodies 



distance of the centres of the molecules ought to depend only 

 in its turn on the mass of these molecules, and on their affi- 

 nity for caloric ; for it is this fluid which, interposing itself be- 

 tween the molecules of these bodies, ought, by the repulsive 

 force which it exerts among its own molecules, to determine 

 the distance in question, according to the quantity and the 

 density to which it may raise itself, when this repulsive force 

 is in equilibrium with the attractive force which the mole- 

 cules of the body exert upon it. With regard to an attrac- 

 tive force which would exert itself immediately between the 

 molecules themselves of the bodies, it could take place be- 

 tween similar molecules, only in virtue of some polarity de- 

 pending on the relative position of the molecules, and on their 

 figure, which cannot be admitted in ductile bodies. There 

 should be still another quality of molecules, which ought to 

 have an influence on the distance of their centres, in the state 

 of equilibrium of the forces which we have mentioned, that is, 

 their volume, from which there ought to result, round their 

 centres, a space more or less great, which can only be occu- 

 pied by caloric, and, consequently, a different limit in the dis- 

 tance of the molecules of caloric from the centre, and a differ- 

 ent action of the molecule upon it. But we may suppose, 

 with sufficient probability, that this volume of the molecules 

 is proportional to their mass, as if the matter of the molecules 

 of bodies was of the same density for all ; and then the in- 

 fluence of the volume of the molecules, in changing the dis- 

 tance of their centres, ought to be included in the function, 

 by which we express the influence of the mass of which we 

 have spoken, and it will only modify this function. This cir- 

 cumstance obliges us, therefore, only to consider separately 

 the mass of the molecules, and their affinity for caloric, in the 

 determination of the total function on which their distance 

 ought to depend, without being able to confine ourselves to a 

 function of the attractive power of the molecule for caloric ; 

 that is, of the product of its mass, by its affinity for that fluid, 

 provided that the law, according to which the distance in 

 question depends on the mass, may be found by the circum- 

 stance indicated, different from that by which it depends on 

 the affinity for caloric. 



