Affinity and Dissected [Structural) Formula. 429 



lecules, each one identical with all the other molecules of the 

 same body, but different from every other kind of molecule), it 

 results that an alteration in the total intrinsic chemical energy 

 present in a given quantity of matter, consisting of one or more 

 homogeneous bodies, whereby a different body or set of bodies is 

 produced, can only be brought about by an alteration in the 

 nature or amount of the relative motions either of the molecules 

 or of their constituent atoms, or of both. Whatever may be the 

 character of the motions before and after the change, they must 

 take place under the influence of forces regulated by definite 

 laws, the law of force regulating the action of one atom or mole- 

 cule on another not being necessarily independent of the nature 

 of the atoms or molecules : e. g. the law of force between two 

 hydrogen atoms is not necessarily the same as that between a 

 hydrogen and an oxygen or a hydrogen and a chlorine atom ; 

 nor is that between two molecules of water necessarily the same 

 as that between a molecule of water and one of hydrochloric acid, 

 or between one of water and one of chloride of sodium. Whatever 

 the nature of these laws of force, however, they must be such 

 that the single resultant force between any two masses of matter, 

 at a distance from one another great as regards the size of the 

 molecules that make up the masses, is inversely proportional 

 to the square of the distance, and directly proportional to the 

 product of the masses (Newton), and such that the single result- 

 ant forces between the constituent molecules themselves are 

 compatible with the phenomena of change of physical state, 

 elasticity, viscosity, cohesion, expansion, diffusion, &c. 



The study of the energy-differences brought about in chemical 

 actions affords a probable means of arriving at the laws which 

 must regulate the mutual action of these hypothetical ultimate 

 atoms of different kinds on one another, and hence of deducing 

 the resultant forces between molecules of various kinds, and 

 consequently of accounting on mechanical grounds for all che- 

 mical and physical phenomena. Should it be hereafter found 

 in this way that such laws of force are possible, a great addition 

 to our knowledge will accrue, and the hypothesis of the atomic 

 constitution of matter will be demonstrated with as much cer- 

 tainty as it is possible that any physical " law n can be demon- 

 strated. On the other hand, should it be clearly proved that 

 the law of force between any given pair of atoms deducible from 

 one set of phenomena is incompatible with that obtained from 

 another set, or that the interatomic forces are irreconcilable 

 with the physical intermodular resultant forces deducible from 

 the study of physical phenomena, or with gravitation, or that 

 any other incompatibilities ensue, it must follow that the pri- 

 mary hypothesis of the atomic constitution of matter is untenable. 



