defects of the earlier
work from an electrical point of view lay chiefly in the difficulty of
measuring the current with sufficient accuracy owing to the imperfect
development of the science of electrical measurement. These difficulties
have been removed by the great advances since 1880, and in particular by
the introduction of accurate standard cells for measurements of
electrical pressure.

S 12. _Griffiths_.--The method adopted by E.H. Griffiths (_Phil.
Trans._, 1893, p. 361), whose work threw a great deal of light on the
failure of previous observers to secure consistent results,
corresponded to the last expression E^2T/R, and consisted in
regulating the current by a special rheostat, so as to keep the
potential difference E on the terminals of the resistance R balanced
against a given number of standard Clark cells of the Board of Trade
pattern. The resistance R could be deduced from a knowledge of the
temperature of the calorimeter and the coefficient of the wire. But in
order to obtain trustworthy results by this method he found it
necessary to employ very rapid stirring (2000 revolutions per minute),
and to insulate the wire very carefully from the liquid to prevent
leakage of the current. He also made a special experiment to find how
much the temperature of the wire exceeded that of the liquid under the
conditions of the experiment. This correction had been neglected by
previous observers employing similar methods. The resistance R was
about 9 ohms, and the potential difference E was varied from three to
six Clark cells, giving a rate of heat-supply about 2 to 6 watts. The
water equivalent of the calorimeter was about 85 grammes, and was
determined by varying the quantity of water from 140 to 260 or 280
grammes, so that the final results depended on a difference in the
weight of water of 120 to 140 grammes. The range of temperature in
each experiment was 14 deg. to 26 deg. C. The rate of rise was
observed with a mercury thermometer standardized by comparison with a
platinum thermometer under the conditions of the experiment. The time
of passing each division was recorded on an electric chronograph. The
duration of an experiment varied from about 30 to 70 minutes. Special
observations were made to determine the corrections for the heat
supplied by stirring, and that lost by radiation, each of which
amounted to about 10% of the heat-supply. The calorimet