f J.C. Jamin
and Amaury, and of many other experimentalists who succeeded Regnault,
appeared to indicate much larger rates of increase than he had found,
but there can be little doubt that the discrepancies of their results,
which often exceeded 5%, were due to lack of appreciation of the
difficulties of calorimetric measurements. The work of Rowland by the
mechanical method was the first in which due attention was paid to the
thermometry and to the reduction of the results to the absolute scale
of temperature. The agreement of his corrected results with those of
Griffiths by a very different method, left very little doubt with
regard to the rate of diminution of the specific heat of water at 20
deg. C. The work of A. Bartoli and E. Stracciati by the method of
mixture between 0 deg. and 30 deg. C., though their curve is otherwise
similar to Rowland's, had appeared to indicate a minimum at 20 deg.
C., followed by a rapid rise. This lowering of the minimum was
probably due to some constant errors inherent in their method of
experiment. The more recent work of Ludin, 1895, under the direction
of Prof. J. Pernet, extended from 0 deg. to 100 deg. C., and appears
to have attained as high a degree of excellence as it is possible to
reach by the employment of mercury thermometers in conjunction with
the method of mixture. His results, exhibited in fig. 6, show a
minimum at 25 deg. C., and a maximum at 87 deg. C., the values being
.9935 and 1.0075 respectively in terms of the mean specific heat
between 0 deg. and 100 deg. C. He paid great attention to the
thermometry, and the discrepancies of individual measurements at any
one point nowhere exceed 0.3%, but he did not vary the conditions of
the experiments materially, and it does not appear that the well-known
constant errors of the method could have been completely eliminated by
the devices which he adopted. The rapid rise from 25 deg. to 75 deg.
may be due to radiation error from the hot water supply, and the
subsequent fall of the curve to the inevitable loss of heat by
evaporation of the boiling water on its way to the calorimeter. It
must be observed, however, that there is another grave difficulty in
the accurate determination of the specific heat of water near 100 deg.
C. by this method, namely, that the quantity actually observed is not
the specific heat _at_ the higher temperature _t_, but the _mean