with a wire guard.

[Illustration: FIG. 15.--Detail of air-resistance thermometer, showing
method of mounting and wiring the thermometer. Parts of the wire guard
and brass guard are shown, cut away so that interior structure can be
seen.]

The details of construction and method of installation are shown in fig.
15. Four strips of mica are inserted into four slots in a hard maple rod
12.5 centimeters long and 12 millimeters in diameter, and around each
strip is wound 5 meters of double silk-covered pure copper wire
(wire-gage No. 30). By means of heavy connecting wires, five of these
thermometers are connected in series, giving a total resistance of the
system of not far from 20 ohms. The thermometer proper is suspended
between two hooks by rubber bands and these two hooks are in turn
fastened to a wire guard which is attached to threaded rods soldered to
the inner surface of the copper wall, thus bringing the center of the
thermometer 3.4 centimeters from the copper wall. Two of these
thermometers are placed in the dome of the calorimeter immediately over
the shoulders of the subject, and the other three are distributed around
the sides and front of the chamber. This type of construction gives
maximum sensibility to the temperature fluctuations of the air itself
and yet insures thorough protection. The two terminals are carried
outside of the respiration chamber to the observer's table, where the
temperature fluctuations are measured on a Wheatstone bridge.

WALL THERMOMETERS.

The wall thermometers are designed for the purpose of taking the
temperature of the copper wall rather than the temperature of the air.
When temperature fluctuations are being experienced inside of the
respiration chamber, the air obviously shows temperature fluctuations
first, and the copper walls are next affected. Since in making
corrections for the hydrothermal equivalent of the apparatus and for
changes in the temperature of the apparatus as a whole it is desirable
to know the temperature changes of the wall rather than the air, these
wall thermometers were installed for this special purpose. In
construction they are not unlike the thermometers used in the air, but
instead of being surrounded by perforated metal they are encased in
copper boxes soldered directly to the wall. Five such thermometers are
used in series and, though attached permanently to the wall, they are
placed in relatively the same position as the air thermometers. Th