er C, fig. 8,
was gilded, and completely surrounded by a nickel-plated steel
enclosure B, forming the bulb of a mercury thermo-regulator, immersed
in a large water-bath maintained at a constant temperature. In spite
of the large corrections the results were extremely consistent, and
the value of the temperature-coefficient of the diminution of the
specific heat of water, deduced from the observed variation in the
rate of rise at different points of the range 15 deg. to 25 deg.,
agreed with the value subsequently deduced from Rowland's experiments
over the same range, when his thermometers were reduced to the same
scale. Griffiths' final result for the average value of the calorie
over this range was 4.192 joules, taking the E.M.F. of the Clark cell
at 15 deg. C. to be 1.4342 volts. The difference from Rowland's value,
4.181, could be explained by supposing the E.M.F. of the Clark cells
to have in reality been 1.4323 volts, or about 2 millivolts less than
the value assumed. Griffiths subsequently applied the same method to
the measurement of the specific heat of aniline, and the latent heat
of vaporization of benzene and water.

[Illustration: FIG. 8.]

S 13. _Schuster and Gannon._--The method employed by A. Schuster and
W. Gannon for the determination of the specific heat of water in terms
of the international electric units (_Phil. Trans._ A, 1895, p. 415)
corresponded to the expression ECT, and differed in many essential
details from that of Griffiths. The current through a platinoid
resistance of about 31 ohms in a calorimeter containing 1500 grammes
of water was regulated so that the potential difference on its
terminals was equal to that of twenty Board of Trade Clark cells in
series. The duration of an experiment was about ten minutes, and the
product of the mean current and the time, namely CT, was measured by
the weight of silver deposited in a voltameter, which amounted to
about 0.56 gramme. The uncertainty due to the correction for the water
equivalent was minimized by making it small (about 27 grammes) in
comparison with the water weight. The correction for external loss was
reduced by employing a small rise of temperature (only 2.22 deg.), and
making the rate of heat-supply relatively rapid, nearly 24 watts. The
platinoid coil was insulated from the water by shellac varnish. The
wire had a length of 760 cms., and the potential differenc