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only show that the laws of thermodynamics are inconsistent 
with the doctrine of the mechanical equivalence of heat. 
10. The argument from the fire syringe I withdraw, as 
inconclusive. But I think my case was sufficiently estab- 
lished without it. 
11. Joule and Scoresby in their paper incorrectly assume 
that if the quantities of electricity in the current at different 
times be represented by (a) and ( b ), the heat varies as 
a 2 to 6 2 . This is only true where the resistance is the same. 
In the case before us the working of the engine introduces 
a fresh element in resistance. 
12. Again, by assuming that ( a — b ) represents diminu- 
tion of quantity of the current, and the diminution in 
the zinc consumed, and the heat converted into useful work, 
they involve the supposition either that less zinc produced 
equal heat, or that heat was changed into useful work which 
was never produced at all, and therefore could not be ab- 
sorbed. In fact there was no proof that any heat was 
absorbed at all. 
13. It is said that in electro-plating, electro-magnetic 
engines, worked by steam, are found more economical than 
batteries. This is in cases where a battery of many cells 
would be required; which is always wasteful, as a large 
number of equivalents of zinc must be consumed to deposit 
one equivalent of silver or other metal. 
14. Besides, there is a far greater advantage in changing 
work into electricity, than electricity into work. In the 
former case all, or nearly all, the work is effective ; in the 
latter, a very small portion of the electricity has hitherto 
been utilised. 
Dr. Hopkinson said that most of Mr. High ton’s objections 
to the mechanical equivalent of heat appear to arise from a 
mistake as to what is meant by the term. The nature of 
this mistake may be best seen in the case of a perfect heat 
