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}.