_,. MOLECULAR FORCE. 



sarily solid, fluid, or aeriform, from tlie circumstance of 

 their having formed the particles of a body in one of 

 these states. 



As this planet a molecule in space is formed of 

 aggregated atoms, and enveloped by its own physical 

 agencies and as it is involved in the infinitely extending 

 influences of other planetary molecules, and thus forms 

 part of a system so the molecules of any mass are 

 grouped into a system or particle, which possesses the 

 great characteristic features of the whole. 



In an aeriform body the particles are in a state of 

 extreme tenuity, the molecules being themselves, by the 

 influence of some repulsive force, just on the verge where 

 cohesion exerts its decaying power. In fluid bodies the 

 attenuation of the particles is less the particles and 

 also the molecules are nearer together, whereas, in the 

 solid body, the forces of cohesion are most strongly ex- 

 erted, and all the molecular conditions brought more 

 powerfully into action. 



Under the term molecular force, we include several 

 agencies, not alike in the phenomena which they 

 exhibit, but which are all-powerful in producing the 

 general characteristics of bodies. These require a 

 somewhat close examination. All the particles of even 

 a solid mass may be brought under conditions on which 

 they are free to move. By heat we can increase the 

 length and thickness of a bar of iron, or any other 

 metal, and at length produce the fluid state, a melted 

 metal flows as freely as water in a stream. Fluids 

 and gases in like manner obey the dispersive influence 

 of caloric. From these and other analogous results wo 

 learn that all bodies have a greater or less degree of 

 porosity. The distance at which the particles of fluid 

 bodies are maintained is strikingly proved by the fact, 

 that hydrated salts dissolved in water occupy no more 

 space than that which is equal to the water contained in 

 the crystalline body : while anhydrous salts dissolve- 



