ed to the
calorimeter. Each experiment lasted about forty minutes, and the rise
of temperature produced was nearly 3 deg. C. The calorimeter contained
about 5 kilogrammes of water, so that the rate of heat-supply was
about 6 calories per second. Joule's final result was 772.55
foot-pounds at Manchester per pound-degree-Fahrenheit at a temperature
of 62 deg. F., but individual experiments differed by as much as 1%.
This result in C.G.S. measure is equivalent to 4.177 joules per
calorie at 16.5 deg. C., on the scale of Joule's mercury thermometer.
His thermometers were subsequently corrected to the Paris scale by A.
Schuster in 1895, which had the effect of reducing the above figure to
4.173.

[Illustration: FIG. 4.]

S 9. _Rowland_.--About the same time H.A. Rowland (_Proc. Amer. Acad._
xv. p. 75, 1880) repeated the experiment, employing the same method,
but using a larger calorimeter (about 8400 grammes) and a petroleum
motor, so as to obtain a greater rate of heating (about 84 calories
per second), and to reduce the importance of the uncertain correction
for external loss of heat. Rowland's apparatus is shown in fig. 5. The
calorimeter was suspended by a steel wire, the torsion of which made
the equilibrium stable. The torque was measured by weights O and P
suspended by silk ribbons passing over the pulleys n and round the
disk kl. The power was transmitted to the paddles by bevel wheels, f,
g, rotating a spindle passing through a stuffing box in the bottom of
the calorimeter. The number of revolutions and the rise of temperature
were recorded on a chronograph drum. He paid greater attention to the
important question of thermometry, and extended his researches over a
much wider range of temperature, namely 5 deg. to 35 deg. C. His
experiments revealed for the first time a diminution in the specific
heat of water with rise of temperature between 0 deg. and 30 deg. C.,
amounting to four parts in 10.000 per 1 deg. C. His thermometers were
compared with a mercury thermometer standardized in Paris, and with a
platinum thermometer standardized by Griffiths. The result was to
reduce the coefficient of diminution of specific heat at 15 deg. C. by
nearly one half, but the absolute value at 20 deg. C. is practically
unchanged. Thus corrected his values are as follows:--

Temperature 10 deg. 15 deg. 20 deg. 25 deg. 30 deg. 35 deg.
Joules per