through the
absorbing system.

The average temperature rise was 3.04 deg. C., the total heat brought away
was therefore (237.63 x 3.04) x 1.0024[17] = 724.1 calories.

Thus in 6 hours there were about 3.7 calories more heat developed inside
the apparatus than were measured by the water-current, a discrepancy of
about 0.5 per cent.

Under ideal conditions of manipulation, the withdrawal of heat from the
calorimeter should be at just such a rate as to exactly compensate for
the heat developed by the resistance-coil. Under these conditions, then,
there would be no heat abstracted from nor stored by the calorimeter and
its temperature should remain constant throughout the whole experiment.
Practically this is very difficult to accomplish and there are minor
fluctuations in temperature above and below the initial temperature
during a long experiment and, indeed, during a short experimental
period. If a certain amount of heat has been stored up in the
calorimeter chamber or has been abstracted from it, there should be
corrections made for the variations in the temperature of the chamber.
Such corrections are impossible unless a proper determination of the
hydrothermal equivalent has been made. A number of experiments to
determine this hydrothermal equivalent have been made and the results
are recorded beyond, together with a discussion of the nature of the
experiments. As a result of these experiments it has been possible to
make correction for the slight temperature changes in the calorimeter.

It is interesting to note that these fluctuations are small and there
may therefore be a considerable error in the determination of the
hydrothermal equivalent without particularly affecting the corrections
applied in the ordinary electrical check-test. The greatest difficulty
experienced with the calorimeter as a means of measuring heat has been
to secure the average temperature of the ingoing water. The temperature
difference between the mass of water flowing through the pipes and the
outer wall of the pipe is at best considerable. The use of the
vacuum-jacketed glass tubes has minimized the loss of heat through this
tube considerably, but it is advisable that the bulb of the thermometer
be placed exactly in the center of the water-tube, as otherwise too high
a temperature-reading will be secured. When the proper precautions are
taken to secure the correct temperature-reading, the results are most
satisfactory.

In testing bot