156 Dr. S. Tolver Preston on some 



that the pressure of the atomic streams over the enlarged 

 surface of contact overcomes the elasticity of form, and the 



Fig. 2. Fig. 3. 



OO CD 



molecules cohere (which one calls "attraction"). As the 

 converse of this, when the molecules are by a tensile- stress 

 pulled nearly apart : then their elasticity of form can make 

 the molecules suddenly spring apart of themselves, as, for 

 instance, " unbreakable " glass flies into dust, when the mole- 

 cular equilibrium is upset by a very sharp blow. Also, in 

 general, if something is broken, the pieces will not readily 

 unite of themselves, when placed in contact. The natural 

 elasticity of shape of the elastic molecules causes an initial 

 repulsion. By suitable assumption regarding thickness, stiff- 

 ness, &c, of these ring-like molecular forms, the differences 

 between the "chemical affinity" of different molecules might 

 doubtless be accounted for. 



Some may think that the above considerations are too 

 simple to contain truth. Nevertheless one may rightly ask 

 whether it is not precisely simplicity that one in general 

 seeks in mechanism ? The elucidation may serve as an 

 initial explanation of certain obscure facts, which may develop 

 itself further. 



Respecting the elasticity of molecules (or atoms) Lord 

 Kelvin makes the following observation : — 



" We are forbidden by the modern physical theory of the 

 conservation of energy to assume inelasticity, or an} 7 thing 

 short of perfect elasticity, in the ultimate molecules" (Phil. 

 Mag. May 1873, p. 329). 



The conception of elastic molecules (also illustrated in a 

 striking manner by spectroscopic observations) appears, as 

 said, to be a very practical conception for Physics, which is 

 much needed. By this assumption the almost inconceivable 

 idea of the sharp blows of " infinitely hard " molecules is 

 avoided. On account of the perfect elasticity, all motions 

 take place with " elegance " and smoothness, which permits 

 a mobile equilibrium in nature, and (without due precautions) 

 may well deceive the senses into the idea that in so-called 

 " space " all is in repose. 



It is a known consequence of the Newtonian law of gra- 

 vitation, that the increase of attraction by diminution of 

 distance is so small that two massive bodies, when they touch 



