MOLECULAR PHYSICS. 



I. GENERAL CONSIDERATIONS. 



THE properties of matter which is not associated with life may, in 

 the present condition of those of the exact Sciences which are 

 founded mainly on experiment, be imperfectly divided into 

 (i) Chemical, (2) Physical, and (3) Molecular. 



(i.) The faculty which the elements possess of combining in 

 definite weight-ratio, gives sameness to the bodies which form the 

 earth : the fact that this ratio is always the same under identical 

 conditions, and often the same under widely different conditions, 

 gives them stability. It is radiation, acting either directly, or 

 through the instrumentality of its offspring, life, which is the main 

 instrument which disturbs the otherwise stable equilibrium of the 

 chemical forces. 



(2.) The faculty which substances have of being the vehicles or 

 temporary abodes of physical forces, may be considered as giving 

 rise to the physical attributes of matter in the more limited sense. 

 These are exhibited in the transmission of pressure in machines, 

 the assumption of mechanical vibration, the electric and magnetic 

 excitement, the absorption and transmission of radiation, and the 

 acquirement of weight when mass is near to mass. The bodies 

 concerned are ponderable. The forces act, or may act, between 

 bodies which are not in direct mechanical contact. Such states 

 and changes are referred to the action of physical forces, which 

 are, therefore, neither more nor less numerous than are the kinds 

 of change which bodies are competent to suffer. The tendency 



