an in turn be connected with _a_ or A, _b_ or
B, etc. The heating of the top of the chair calorimeter is controlled by
the point 5 on the rheostat R_{2}, the rear by the point 4, the front by
the point 3, and the bottom by the point 2. Point 1 is used for heating
the air entering the calorimeter by means of an electric lamp placed in
the air-pipe, as shown in fig. 25.

The warming of the electrical reheater placed in the water-circuit just
before the water enters the calorimeter is done by an electrical current
controlled by the resistance R_{1}. This R_{1} is connected on one end
directly with the 110-volt circuit and the current leaving it passes
through the resistance inside the heater in the water-current. The two
heaters, one for each calorimeter, are indicated on the diagram above
and below the switch S_{9}. The disposition of the switches is such as
to make it possible to use alternately the reheaters on either the bed
or the chair calorimeter, and the main resistance R_{1} suffices for
both.

WHEATSTONE BRIDGES.

For use in measuring the temperature of the air and of the copper wall
of the calorimeters, as well as the rectal temperature of the subject, a
series of resistance thermometers is employed. These are so connected
on the observer's table that they may be brought into connection with
two Wheatstone bridges, W_{1} and W_{2}. Bridge W_{1} is used for the
resistance thermometers indicating the temperature of the wall and the
air. Bridge W_{2} is for the rectal thermometer. Since similar
thermometers are inserted in both calorimeters, it is necessary to
introduce some switch to connect either set at will and hence the
double-throw switches S_{1}, S_{2}, and S_{3} allow the use of either
the wall, air, or rectal thermometer on either the bed or chair
calorimeter at will. Since the bridge W_{1} is used for measuring the
temperature of both the wall and the air, a fourth double-pole switch,
S_{4}, is used to connect the air and wall thermometers alternately. The
double-contact key, K_{1}, is connected with the bridge W_{1} and is so
arranged that the battery circuit is first made and subsequently the
galvanometer circuit. A similar arrangement in K_{2} controls the
connections for the bridge W_{2}.

GALVANOMETER.

The galvanometer is of the Deprez-d'Arsonval type and is extremely
sensitive. The sensitiveness is so great that it is desirable to
introduce a resistance of some 500 ohms into the thermal-j