Conditions of Molecular Action. 361 



been referred to the possession by the material particles of im- 

 ponderable atmospheres with various properties*. 



It is not intended in the present paper to enter upon the dis- 

 cussion of the atomic or molecular constitution of bodies ; and 

 although the modes in which matter is related to, or affected by, 

 heat and other physical forces are intimately connected with the 

 subject, and will probably eventually throw much light upon 

 molecular actions, for the present these relations will only be in- 

 cidentally mentioned, and the substance of these remarks will be 

 restricted to more material reactions. 



It is convenient also to mark off chemical from purely mole- 

 cular actions; and this may be roughly effected by stating that, 

 whether or not chemical combination results from molecular ac- 

 tions, the peculiar forces of which we shall treat do not take part 

 in the chemical reactions, nor assist in binding together the ele- 

 ments of the resulting compounds. The force of cohesion also, 

 which binds together the particles of the same substance, will 

 not here be considered. We shall be mainly concerned with the 

 action of different substances upon one another through the in- 

 tervention of certain molecular forces or affinities, or, in other 

 words, with the relations to be observed between the particles of 

 various substances, apart from their chemical activities, when 

 they are brought into close proximity with one another. 



There are many groups of these actions, and chief amongst 

 them the so-called catalytic or contact actions. Certain of them 

 will now be brought closely under review in an endeavour to 

 ascertain the special circumstances under which molecular ener- 

 gies come into play. 



It may be well first, however, to state briefly what is known 

 of the forces in question ; and the following propositions respect- 

 ing them will probably include all that can at present be affirmed 

 about them : — 



(1) That molecular influence depends essentially upon the 

 elementary nature of bodies. 



(2) That it acts without regard to mass. 



(3) That it increases inversely as the distance, at some enor- 

 mous ratio. 



(4) That its action is in some way affected by calori6c, elec- 

 tric, and probably by luminous vibrations, and by chemical 

 affinity, 



(5) That it does not seem to differ in kind from the attraction 

 of cohesion, which binds together the particles of the same 

 substance. 



(6) That chemical affinity may be similar in kind, but that it 



* Norton, Phil. Mag. S. 4. Nos. 188 &c. ; and Maxwell, Phil. Mag. S. 4. 

 No. 194, (vol. xxix.) p. 152. 



