hamber.

The chamber is illuminated by a small glass door in the food aperture.
This is a so-called "port" used on vessels. Sufficient light passes
through this glass to enable the subject to see inside the calorimeter
without difficulty and most of the subjects can read with comfort. If an
electric light is placed outside of the window, the illumination is very
satisfactory and repeated tests have shown that no measurable amount of
heat passes through the window by placing a 32 c. p. electric lamp 0.5
meter from the food aperture outside. More recently we have arranged to
produce directly inside the chamber illumination by means of a small
tungsten electric lamp connected to the storage battery outside of the
chamber. This lamp is provided with a powerful mirror and a glass shade,
so that the light is very bright throughout the chamber and is
satisfactory for reading. It is necessary, however, to make a correction
for the heat developed, amounting usually to not far from 3 calories per
hour.

By means of a hand microphone and receiver, the subject can communicate
with the observers outside at will. A push-button and an electric bell
make it possible for him to call the observers whenever desired.

HEAT-ABSORBING CIRCUIT.

To bring away the heat produced by the subject, it is highly desirable
that a constant flow of water of even temperature be secured. Direct
connection with the city supply is not practicable, owing to the
variations in pressure, and hence in constructing the laboratory
building provision was made to install a large tank on the top floor,
fed with a supply controlled by a ball-and-cock valve. By this
arrangement the level in the tank is maintained constant and the
pressure is therefore regular. As the level of the water in the tank is
approximately 9 meters above the opening in the calorimeter, there is
ample pressure for all purposes.

[Illustration: FIG. 14.--Schematic diagram of water circuit for
heat-absorbers of calorimeter. A, constant-level tank from which water
descends to main pipe supplying heat-absorbers; _a_, valve for
controlling supply from tank A; B, section of piping passing into cold
brine; _b_, valve controlling water direct from large tank A; _c_, valve
controlling amount of water from cooling section B; C, thermometer at
mixer; D, electric heater for ingoing water; E, thermometer for ingoing
water; _d d d_, heat-absorbers inside calorimeter; F, thermometer
indicating tempera