151 
engine, of which q and t 0 are the absolute temperatures of 
the source and refrigerator. Then from every unit of heat 
leaving the source we obtain 
h ~ tp 
h 
J 
units of work. 
Now 
this a quantity variable with q and t 0 ; it would be similar 
to most of Mr. Highton’s arguments to infer that from a 
given quantity of heat a variable quantity of work could be 
obtained. But, of course, the case really is, that, of the unit 
of heat leaving the source, -j- is lost in the refrigerator, 
h 
whilst — - - ° disappears as heat and is converted into the work 
done, and the principle of the equivalence of heat and work 
asserts that J is constant. It will be seen that this is the 
mistake Mr. High ton makes in his paper in the Journal of 
Science (end of article G). He seems there to imagine it 
stated, that the work done is equivalent to the whole heat 
thrown into the gas, and he fails to perceive that a certain 
portion is used to raise the temperature of the air or turpen - 
tine. 
This will make my criticism of his paper in the Chemical 
News clearer. Mr. Highton argued against the mechanical 
equivalent, and what I pointed out was, that the chemical 
energy, which was converted into mechanical effect and not 
used to heat the wire, was proportional to a — h, that there- 
fore, in order to prove that there was no mechanical equiva- 
lent, Mr. Highton must show is variable. I do not as- 
sert that a badly constructed engine will get as much heat 
from fuel as a good one, but merely that the work done 
and the heat, which has disappeared as heat and been 
converted into work, are in a constant ratio. 
Now as regards Mr. Highton’s argument from the case of 
elastic wires — that the wire will be cooled when stretched 
follows from the two laws of thermodynamics, a proof may 
be seen in Tait’s Therm odynamics, p. 105. Mr. Highton 
