1878.] Past Changes in the Universe. 371 
the gravific medium again in a cyclical process, in the ope- 
ration of elevating the materials in opposition to the dynamic 
aCtion of the gravific medium which tends to urge them 
towards the earth. If, instead of elevating materials, the 
work be done in friction, as in dragging masses (vehicles, 
&c.) along the earth’s surface, then the waves of heat due 
to the fridtion are radiated into the media of space, and, 
becoming naturally dissipated in the gravific medium through 
which they have to pass, the energy thus finally returns to 
this medium, to be available for utilisation again. Winds 
or currents of air are due diredtly (as is known) to variations 
of pressure in the earth’s atmosphere, which re-adjust 
themselves through the aCtion of gravit}^. The gravific 
medium is therefore the agent direddly concerned in pro- 
ducing the current of air or wind, and therefore is the 
motive agent concerned in developing motion in the ma- 
chinery driven through the intervention of the wind. In 
the case of the ship propelled by the wind, the power is 
converted into heat in the passage of the ship through the 
water. The heat then passes in waves to the media in 
space, or is dissipated in the souree whence it was derived 
in a cyclical process. It should be observed that all these 
deductions are necessarily true on the acceptance of the 
explanation of the mechanism of gravity afforded by the 
physical theory. 
There can be little doubt that the explanation of gravity 
(the fundamental agency in Nature) will naturally and 
inevitably entail with it, in principle, analogous explanations 
of the other molecular motions (“chemical” reactions, &c.). 
Thus the operation of the steam-engine will show itself as 
a cyclical process, the motion passing from the media in 
space to the coal, and thence (in a circle) to the media in 
space in the various operations of the engine.* Thus con- 
siderations of great practical interest present themselves on 
the recognition of the existence of the stores of concealed 
motion in space revealed by the kinetic theory of gravita- 
tion, and problems of the highest practical importance may 
suggest themselves as to possible methods of utilising this 
store of motion to greater advantage than at present. 
There might be a tendency to regard considerations of this 
nature (independently of their truth or error) as in some 
degree occult. This could only arise from the kind of pre- 
judice that tends to beset every new path, or possibly in the 
* See also a paper in Philosophical Magazine for April last (“ The Bearing 
of the Kinetic Theory of Gravitation on the Phenomena of ‘ Cohesion ’ and 
Chemical A&ion ’ ”). 
2 B 2 
