resort to the use of a wooden chair,
relying upon its changes in weight as noted by the balance to aid us in
apportioning the water vaporized between the man and his clothing and
the chair.

The walls of the chamber are semi-rigid. Owing to the calorimetric
features of this apparatus, it is impracticable to use heavy
boiler-plate or heavy metal walls, as the sluggishness of the changes in
temperature, the mass of metal, and its relatively large hydrothermal
equivalent would interfere seriously with the sensitiveness of the
apparatus as a calorimeter. Hence we use copper walls, with a fair
degree of rigidity, attached to a substantial structural-steel support;
and for all practical purposes the apparatus can be considered as of
constant volume. Particularly is this the case when it is considered
that the pressure inside of the chamber during an experiment never
varies from the atmospheric pressure by more than a few millimeters of
water. It is possible, therefore, from the measurements of this chamber,
to compute with considerable accuracy the absolute volume. The apparent
volume has been calculated to be 1,347 liters.

OPENINGS IN THE CHAMBER.

In order to communicate with the interior of the chamber, maintain a
ventilating air-current, and provide for the passage of the current of
water for the heat-absorber system and the large number of electrical
connections, a number of openings through the walls of the chamber were
necessary. The great importance of maintaining this chamber absolutely
air-tight renders it necessary to minimize the number of these openings,
to reduce their size as much as possible, and to take extra precaution
in securing their closure during an experiment. The largest opening is
obviously the trap-door at the top through which the subject enters,
shown in dotted outline in fig. 7. While somewhat inconvenient to enter
the chamber in this way, the entrance from above possesses many
advantages. It is readily closed and sealed by hot wax and rarely is a
leakage experienced. The trap-door is constructed on precisely the same
plan as the rest of the calorimeter, having its double walls of copper
and zinc, its thermal-junction system, its heating wires and
connections, and its cooling pipes. When closed and sealed, and the
connections made with the cooling pipes and heating wires, it presents
an appearance not differing from any other portion of the calorimeter.

The next largest opening is the fo