FREE AND PERFECTLY ELASTIC MOLECULES IN A STATE OF MOT [ON. 51 
This is the interpretation of M. Clapeyron’s fundamental position* applied to the 
hypothetical medium. M. Clapeyron assumes that the quantity of heat taken from 
the body A (p. 349, ‘ Taylor’s Memoirs ’) during the expansion from C to E is 
necessarily equal to the quantity given to the body B during compression from F 
to K, and that from E to F and K to C no heat is taken from or given to the volume 
of gas, a proportion only of the sensible heat being reduced to a latent form and 
again thrown out. Thus, there appears the anomaly of the mechanical force S being- 
exerted or generated without any loss of heat. M. Clapeyron’s view is here so much 
at variance with the vis viva theory of heat that it seemed proper to enter into a full 
explanation of the same condition in the hypothetical medium. The case is very 
instructive, and throws light on the vis viva theory, which is at the same time the 
means of clearing up the anomaly in causation of mechanical force seeming to be 
generated without expenditure of heat. M. Clapeyron’s conclusions, so far as gases 
are concerned, are quite independent of any hypothesis, and seem to be strictly 
deduced from the laws of Mariotte and Dalton and Gay-Lussac combined with 
the relation that has been found to subsist between simultaneous increments of 
sensible and of latent heat. It is satisfactory to observe that they agree, so far as 
■they go, with the physical properties of the medium. 
Note G .— Objection to Theory. 
The only difficulty I can discover in the vis viva theory of heat applies in some 
measure to the undulatory theory of light. The ethereal medium that transmits the 
undulations is affected by vibrations of the elements of matter, but there is not the 
least symptom of it affecting by its resistance the planetary motions, and yet theory 
shows that it must permeate through the very substance and heart of all bodies with 
such quick and subtle power as not in any sensible manner to be affected in its 
equilibrium by any part of their motion except what is vibratory. Now, the vis viva 
theory of heat shows that the greatest ordinary velocities of this vibratory motion 
do not much exceed 2000 feet per second, but the velocity of the earth in its orbit 
is upwards of 50 times this amount. In the first case, if a hot body were isolated 
from all surrounding matter, the whole of its motion -would be withdrawn from it in a 
very short time by the ethereal medium. This we can affirm inductively from the 
laws of the radiation of heat. In the second case not the slightest resistance is made 
manifest. The ether only affects and is affected by vibratory motion. Any other 
kind, however great, it neither affects nor is affected by. What are we to infer from 
this incongruity 1 If vibratory motion differed in no other point from the rectilinear 
and rotatory motion of masses of matter, than in the sudden change of direction, it is 
plain that if there was no resistance in the one case there could be no resistance in 
the other, and vice versa. We are, therefore, compelled to infer that the disturbance 
* Essay on the motive power of heat, ‘ Journ. Polyt.,’ translated in ‘ Taylor’s Memoirs,’ vol. 1, p. 349. 
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