184 Atomic Matter and Luminiferous Ether. (April, 
touch the same horizontal and lower plane at the same 
time, that time being the same as would be occupied by the 
fall of a ball in a vertical line from the cannon’s mouth to 
the same horizontal plane. ‘To-and-fro vibrations would, in 
this sense, be unaffected by transverse vibrations which are 
at right angles, and thus to-and-fro vibrations of gravity 
would be unaffected by the transverse vibrations of light, &c. 
Gravitation vibrations, if ultimately passing into space, 
would cause a body to lose weight. 
It is supposed that suns and planets lose heat from the 
motion they impart to the rays or vibrations of radiant heat, 
but the effects of the sun’s and planets’ loss of heat are not 
now astronomically observable, and the effects of the loss 
of gravity and of heat may perhaps be observed simulta- 
neously. As, however, gravity and heat rays are not 
of the same kind, there is probably a difference in the 
rate of their dissipation, and the force of gravity may be 
the weakest but most enduring. In the sunbeam there are 
both light and heat rays whose vibrations are of the same 
kind. Incandescent bodies yield similar duplex rays, but 
their radiant light is extinguished before their radiant heat ; 
and we may conclude that if the sun’s condition changes it 
will be dark long before it be cold; and as similar vibrations 
are found to dissipate energy, at different rates, dissimilar 
vibrations most probably follow the same rule. 
According to the axiom of the conservation of energy, the 
rule as to its dissipation is, that energy is parted with or ab- 
sorbed by work done. A feeble force, or one able to perform 
little work, absorbs only feeble energy to originate; con- 
versely, a powerful force owes its origin to much energy, 
and the most powerful force may be the first dissipated. 
In calling gravitya feeble force, the necessity of measuring 
a force becomes apparent. Light, heat, electricity, &c., are 
termed imponderable forces. This phrase, by implication, 
admits the possibility of ponderable forces. Is oxygen, for 
example, a ponderable force? An examination of this 
question will serve to show the sense in which these terms 
should be used. Assume oxygen to be a ponderable force, 
and it is at present impossible to refute the assumption by 
experiment. Andrews compressed oxygen to about the 
density of water, and it remained then, as ever, invisible and 
intangible, except by its forces, its ponderability included. 
Elements unite with oxygen, and fresh substances of dif- 
ferent properties are produced. Heat unites with or is 
absorbed by ice, and water is produced. ‘The allotropic 
forms of phosphorus and of sulphur, and many other 
a 
