322 FRAGMENTS OF SCIENCE. 
into the heat evolved by the passage of the currents of in- 
duction through its coils; and, on the other hand, that 
the motive power of the electro-magnetic engine is obtained 
at the expense of the heat due to the chemical reaction of 
the battery by which it is worked."* It is needless to 
dwell upon the weight and importance of this statement. 
Considering the imperfections incidental to a first 
determination, it is not surprising that the " mechanical 
values of heat," deduced from the different series of ex- 
periments published in 1843, varied widely from each 
other. The lowest limit was 587, and the highest 1,026 
foot-pounds, for one degree Fahrenheit of temperature. 
One noteworthy result of his inquiries, which was 
pointed out at the time by Mr. Joule, had reference to 
the exceedingly small fraction of the heat actually con- 
verted into useful effect in the steam-engine. The 
thoughts of the celebrated Julius Robert Mayer, who was 
then engaged in Germany upon the same question, had 
moved independently in the same groove; but to his 
labors due reference will be made on a future occasion. f 
In the memoir now referred to, Mr. Joule also announced 
that he had proved heat to be evolved during the 
passage of water through narrow tubes; and he deduced 
from these experiments an equivalent of 770 foot-pounds, a 
figure remarkably near the one now accepted. A detached 
statement regarding the origin and convertibility of animal 
heat strikingly illustrates the penetration of Mr. Joule, 
and his mastery of principles, at the period now referred 
to. A friend had mentioned to him Haller's hypothesis, 
that animal heat might arise from the friction of the blood 
in the veins and arteries. " It is unquestionable," writes 
Mr. Joule, " that heat is produced by such friction; but it 
must be understood that the mechanical force expended in 
the friction is a part of the force of affinity which causes 
the venous blood to unite with oxygen, so that the whole 
heat of the system must still be referred to the chemical 
changes. But if the animal were engaged in turning a 
piece of machinery, or in ascending a mountain, I appre- 
hend that in proportion to the muscular effort put forth 
for the purpose, a diminution of the heat evolved in the 
system by a given chemical action would be experienced." 
* Phil. Mag., May, 1845. f See the next Fragment, 
