188 Atomic Matter and Luminiferous Ether. (April, 
of position” is due to the fact that the body, in moving, 
will receive, from the then existent vibrations, an energy the 
exact equivalent of the vibrations arrested, and probably, 
but not necessarily, the equivalent of the energy absorbed 
in placing it in position. 
That energy of position is really due to the circumstances 
surrounding the position, from time to time, is perhaps still 
more evident from considering the difference in weight of 
the same body at the earth’s poles and equator, 194 lbs. in 
the former position weighing only 193 in the latter one. 
But one of the clearest proofs is that of an ele¢tro-magnet 
and an iron bar. For convenience we may imagine the 
magnet placed vertically, and the iron bar upon it. The 
bar, being raised, acquires an energy of position due both to 
the magnetic attraction and force of gravity. It absorbs 
energy to raise it, and evolves its equivalent in its descent. 
But it may be raised whilst the electric current is stopped, 
and fall: whilst it is passing. It would then evolve more 
energy in falling than was employed in raising it. Vzce versa 
if raised whilst the current passes, and falling when it is 
stopped ; and, evidently too, variations in the electric current 
would vary either the energy required to raise the bar to any 
given position, or the energy of position after the bar is 
raised. Briefly, then, energy of position of this kind is in 
every case dependent on the forces or motion of the present, 
and is disconnected from the forces, or motion, or energy of 
the past; in its nature it is variable and accidental. 
But latent or potential energy of another kind may and 
probably does exist, viz., the latent energy of a bent spring; 
but this raises the question of elasticity asa quality of tangible 
matter, and it is difficult or impossible to comprehend the 
possibility of this form of energy, except the quality of 
elasticity be assumed. A compressed gas on the atomic 
hypothesis is elastic because the paths of its atoms are 
shortened, and their impacts more frequent; it is not a 
quality of the gas, but of its mechanical structure, and is 
dependent on the motion of its particles. But on appealing 
to experimental results, we find when any tangible 
substance is broken up the transmission of vibration is 
interrupted. Beginning with a cracked bell, we may pass to 
Tyndall’s recent proof that alternate layers of gas of 
different densities retard sound, and twenty-five alternate 
layers of coal gas and carbonic acid gas, forming a column 
about four feet thick, he shows are impervious to sound. 
The same gases diffused through each other are pervious to 
sound. Similar kind of phenomena occur in similar 
