Dynamical Theories of Gravitation. 157 



each other, attract each other so much the less the smaller 

 they are ; which one at once sees in the case of two spheres in 

 contact, and can also demonstrate for bodies of other shapes. 

 If, therefore, one attributes a massive structure to molecules, 

 then, for the explanation of cohesion and chemical affinity, 

 forces must be assumed which, by diminution of distance, 

 increase quicker in intensity than according to the Newtonian 

 gravitation law. On the other hand, the attraction of two 

 cylinders of finite length and infinitely small section becomes 

 infinitely great so soon as they touch each other. It is 

 possible, therefore, on the basis of the here assumed open 

 structure of matter, also to account for cohesion, adhesion, 

 and chemical affinity, without necessarily having recourse to 

 forces which, with diminished distance, augment quicker in 

 intensity than the Newtonian law of gravity demands. 



The Theory of Isenkrahe. 



Two years after the present writer's first published paper, 

 appeared the gravitation theory of Dr. Isenkrahe*, which 

 attempts an explanation of gravity based on the kinetic theory 

 of gases, and which seems in Germany to have become very 

 well known. The author of this theory makes no mention of 

 my theory, and it doubtless escaped his attention at that time. 



The gravitation theory of Dr. Isenkrahe is founded on 

 inelastic collision, which obviously involves the annihilation 

 of energy, whereby the gas producing gravity would, after a 

 certain (even very long) epoch, come to rest, and so gravi- 

 tation cease to exist. 



In a plausible enough way (at first sight at least) the 

 author despises elasticity as a qualitas occulta, which, as he 

 thinks, needs an explanation just as much as gravity itself. 

 It seems, however, to have been overlooked that elasticity (at 

 the encounters of molecules) is already demonstrated to exist 

 by the principle of the conservation of energy, and of the 

 centre of mass. The explanation of elasticity is a deeper one 

 than the explanation of gravitation : therefore let us advance 

 from step to step forward in the elucidation, without pushing 

 on in too great a hurry. 



All the consequences of the kinetic theory of gases are 

 already built on the assumption of elasticity : the application 

 of this principle to the smaller particles is therefore to be 

 viewed as a perfectly natural and logical consequence. In 

 fact the gravitation pressure by the encounters of elastic 



* Das Rathsel von der Schiverkraft, by Dr. C. Isenkrahe. (Vieweg & 

 Sohn, Braunschweig, 1879.) 



