definite determination of the mechanical value of heat.

At the meeting of the British Association at Cork, on August 21, 1843,
he read his paper "On the Calorific Effects of Magneto-Electricity,
and on the Mechanical Value of Heat." The paper gives an account of an
admirable series of experiments, proving that _heat is generated_ (not
merely _transferred_ from some source) by the magneto-electric machine.
The investigation was pushed on for the purpose of finding whether a
_constant ratio exists between the heat generated and the mechanical
power_ used in its production. As the result of one set of
magneto-electric experiments, he finds 838 foot pounds to be the
mechanical equivalent of the quantity of heat capable of increasing the
temperature of one pound of water by one degree of Fahrenheit's scale.
The paper is dated Broomhill, July, 1843, but a postscript, dated
August, 1843, contains the following sentences:

"We shall be obliged to admit that Count Rumford was right in
attributing the heat evolved by boring cannon to friction, and not (in
any considerable degree) to any change in the capacity of the metal. I
have lately proved experimentally that _heat is evolved by the passage
of water through narrow tubes_. My apparatus consisted of a piston
perforated by a number of small holes, working in a cylindrical glass
jar containing about 7 lb. of water. I thus obtained one degree of heat
per pound of water from a mechanical force capable of raising about 770
lb. to the height of one foot, a result which will be allowed to be very
strongly confirmatory of our previous deductions. I shall lose no time
in repeating and extending these experiments, being satisfied that the
grand agents of nature are, by the Creator's fiat, _indestructible_, and
that wherever mechanical force is expended, an exact equivalent of heat
is _always_ obtained."