102 MOLECULAR FORCES. SECT. XIV. 



SECTION XIV. 



Molecular Forces Permanency of the ultimate Particles of Matter 

 Interstices Mossotti's Theory Rankin's Theory of Molecular Vor- 

 tices Gases reduced to Liquids by Pressure Gravitation of Particles 

 Cohesion Crystallization Cleavage Isomorphism Minuteness 

 of the Particles Height of Atmosphere Chemical Affinity De- 

 finite Proportions and Relative Weights of Atoms Faraday's Discovery 

 with regard to Affinity Capillary Attraction. 



THE oscillations of the atmosphere, and its action upon the rays 

 of light coming from the heavenly bodies, connect the science of 

 astronomy with the equilibrium and movements of fluids and the 

 laws of molecular attraction. Hitherto that force has been under 

 consideration which acts upon masses of matter at sensible dis- 

 tances ; but now the effects of such forces are to be considered as 

 act at inappreciable distances upon the ultimate molecules of 

 material bodies. 



All substances consist of an assemblage of material particles, or 

 molecules, which are far too small to be visible by any means 

 human ingenuity has yet been able to devise, and which are much 

 beyond the limits of our perceptions. They neither can be created 

 nor destroyed ; bodies may be burned, but their particles are not 

 consumed they are merely liberated from one combination to 

 enter into another, nor are their peculiar properties ever changed ; 

 whatever combinations they may enter into, they are ever and 

 invariably the same. 



Since every known substance may be reduced in bulk by pres- 

 sure, it follows that the particles of matter are not in actual 

 contact, but are separated by interstices ; and it is evident that the 

 smaller the interstitial spaces the greater the density. These 

 spaces appear to be filled with air in some cases, as may be 

 inferred from certain semi-opaque minerals and other substances 

 becoming transparent when plunged into water. Sometimes they 

 may possibly contain some unknown and highly elastic fluid, 

 such as Sir David Brewster has discovered in the minute cavities 

 of various minerals, which occasionally causes them to explode 



