ng, under
comparable circumstances, the same calorific power as the voltaic
electricity.

"Professor Jacobi, of St. Petersburg, bad shown that the motion of an
electro-magnetic machine generates magneto-electricity in opposition
to the voltaic current of the battery. The author had observed the same
phenomenon on arranging his apparatus as an electro-magnetic machine;
but had found that no additional heat was evolved on account of the
conflict of forces in the coil of the electro-magnet, and that the heat
evolved by the coil remained, as before, proportional to the square of
the current. Again, by turning the machine contrary to the direction of
the attractive forces, so as to increase the intensity of the voltaic
current by the assistance of the magneto-electricity, he found that the
evolution of heat was still proportional to the square of the current.
The author discovered, therefore, that the heat evolved by the voltaic
current is invariably proportional to the square of the current, however
the intensity of the current may be varied by magnetic induction. But
Dr. Faraday has shown that the chemical effects of the current
are simply as its quantity. Therefore he concluded that in the
electro-magnetic engine a part of the heat due to the chemical actions
of the battery is lost by the circuit, and converted into mechanical
power; and that when the electro-magnetic engine is turned CONTRARY to
the direction of the attractive forces, a greater quantity of heat is
evolved by the circuit than is due to the chemical reactions of the
battery, the over-plus quantity being produced by the conversion of the
mechanical force exerted in turning the machine. By a dynamometrical
apparatus attached to his machine, the author has ascertained that,
in all the above cases, a quantity of heat, capable of increasing the
temperature of a pound of water by one degree of Fahrenheit's scale, is
equal to the mechanical force capable of raising a weight of about eight
hundred and thirty pounds to the height of one foot."(2)

JOULE OR MAYER?

Two years later Joule wished to read another paper, but the chairman
hinted that time was limited, and asked him to confine himself to
a brief verbal synopsis of the results of his experiments. Had the
chairman but known it, he was curtailing a paper vastly more important
than all the other papers of the meeting put together. However, the
synopsis was given, and one man was there to hear it who had t