rise of temperature for two
or more widely different values of the flow of liquid. An example
taken from the _Electrician_, September 1897, of one of the earliest
experiments by this method on the specific heat of mercury will make
the method clearer. The flow-tube was about 1 metre long and 1 millim.
in diameter, coiled in a short spiral inside the vacuum jacket. The
outside of the vacuum jacket was immersed in a water jacket at a
steady temperature equal to that of the inflowing mercury.

SPECIFIC HEAT OF MERCURY BY CONTINUOUS ELECTRIC METHOD

+-----------+---------------+------+-------------+----------------+
|Flow of Hg.| Rise of Temp. |Watts.| Heat-loss. | Specific Heat. |
+-----------+---------------+------+-------------+----------------+
| gm./sec. | d[theta] | EC | hd[theta] | Per gm. deg. |
| 8.753 | 11.764 |14.862| 0.655 | \ .13780 joules|
| 4.594 | 12.301 | 7.912| 0.865 | / .03297 cals. |
+-----------+---------------+------+-------------+----------------+

It is assumed as a first approximation that the heat-loss is
proportional to the rise of temperature _d[theta]_, provided that
_d[theta]_ is nearly the same in both cases, and that the distribution
of temperature in the apparatus is the same for the same rise of
temperature whatever the flow of liquid. The result calculated on
these assumptions is given in the last column in joules, and also in
calories of 20 deg. C. The heat-loss in this example is large, nearly
4.5% of the total supply, owing to the small flow and the large rise
of temperature, but this correction was greatly reduced in subsequent
observations on the specific heat of water by the same method. In the
case of mercury the liquid itself can be utilized to conduct the
electric current. In the case of water or other liquids it is
necessary to employ a platinum wire stretched along the tube as
heating conductor. This introduces additional difficulties of
construction, but does not otherwise affect the method. The absolute
value of the specific heat deduced necessarily depends on the absolute
values of the electrical standards employed in the investigation. But
for the determination of relative values of specific heats in terms of
a standard liquid, or of the variations of specific heat of a liquid,
the method depends only on the constancy of the standards, which