1874.] Atomic Matter and Luminiferous Ether. 185 
instances, will occur to every reader’s mind where a substance 
of different properties is produced by the action or absorp- 
tion of an imponderable force. A ponderable force would 
only add weight. If ice became heavier in melting we 
should say matter was added to it, only because it increased 
in weight. Radiant heat adds volume as well as sensible 
heat to the body that absorbs it, so that the addition of two 
qualities to a substance by the action of one force is not 
rare. Hence, in the attempt to prove that gravity is a 
feeble force, the difficulties of measuring forces by gravity, 
and of the conception of forces as apart from matter, must 
be remembered. 
In many respects gravity well deserves to be called a feeble 
force. Our atmosphere sustains a load of 15 Ibs. to the square 
inch ; we call it a great load,—+. ¢., a great result of gravity, 
—but do not equally appreciate the-effort of the air in 
resisting it; it requires an _intelleCtual effort to say the two 
are equal, and then the magnitude of this effort of gravity 
does not seem comparatively large. 
Prof. Osborne Reynolds has recently shown that a small 
glass tube, sufficiently strong to be safely used as a gun, 
with gunpowder, so as to propel little brass rods through a 
half-inch board, was shattered into the minutest dust when 
partly filled with water and acharge of electricity discharged 
through it. A similar result, if obtained by gravity, would 
have required the pressure of a weight to be measured by 
many tons on the square inch. ‘This experiment was made 
to illustrate the effect of lightning upon splitting trees, 
shattering stones, &c., and Faraday showed some years ago 
that more electricity was concerned in a dew-drop than ever 
was manifested in a thunderstorm. Many trees and stones 
are often shivered to fragments by one storm, showing that 
an equivalent to enormous mechanical or gravitation forces 
is latent in a part of one of the forces that builds up a drop 
of water. 
Heat expands bodies, and requires an enormous me- 
chanical or gravitation force to resist it. The rays of the 
sunbeam, if converted into mechanical force, would far 
exceed anything we can realise; and heat may be said to 
act paradoxically. Its absorption develops mechanical 
force, and so does its subtraction from freezing water and 
from solidifying bismuth. 
The sunbeam also contains actinic or chemical rays, 
probably the most energetic of all, and for the me- 
chanical equivalent of chemical energy we may again go 
to Faraday for an illustration. 
