The measurements of the temperature of the respiration chamber, of the
water-current, and of the body temperature of the man, as well as the
heating and cooling of the air-spaces about the calorimeter, are all
under the control of the physical assistant. The apparatus for these
temperature controls and measurements is all collected compactly on a
table, the so-called "observer's table." At this, the physical assistant
sits throughout the experiments. For convenience in observing the
mercurial thermometers in the water-current and general inspection of
the whole apparatus, this table is placed on an elevated platform, shown
in fig. 3. Directly in front of the table the galvanometer is suspended
from the ceiling and a black hood extends from the observer's table to
the galvanometer itself. On the observer's table proper are all the
electrical connections and at the left are the mercurial thermometers
for the chair calorimeter. Formerly, when the method of alternately
cooling and heating the air-spaces was used, the observer was able to
open and close the water-valves without leaving the chair.
The observer's table is so arranged electrically as to make possible
temperature control and measurement of either of the two calorimeters.
It is impossible, however, for the observer to read the mercurial
thermometers in the bed calorimeter without leaving his chair, and
likewise he must occasionally alter the cooling water flowing through
the outer air-spaces by going to the bed calorimeter itself. The
installation of the electric-resistance thermometers connected with the
temperature recorder does away with the reading of the mercurial
thermometers, save for purposes of comparison, and hence it is
unnecessary for the assistant to leave the chair at the observer's table
when the bed calorimeter is in use. Likewise the substitution of the
method of continuously cooling somewhat the air-spaces and reheating
with electricity, mentioned on page 18, does away with the necessity for
alternately opening and closing the water-valves of the chair
calorimeter placed at the left of the observer's table.
[Illustration: FIG. 17.--Diagram of wiring of observer's table. W_{1},
W_{2}, Wheatstone bridges for resistance thermometers; K_{1}, K_{2},
double contact keys for controlling Wheatstone circuits; S_{1}, S_{2},
S_{3}, double-pole double-throw switches for changing from chair to bed
calorimeter; S_{4}, double-pole double-throw switch for changing from
wall to air thermometers; G, galvanometer; R_{2}, rheostat. 1, 2, 3, 4,
5, wires connecting with resistance-coils A B D E F and _a b d e f_;
S_{2}, 6-point switch for connecting thermal-junction circuits of either
bed or chair calorimeter with galvanometer; S_{10}, 10-point
double-throw switch for changing heating circuits and thermal-junction
circuits to either chair or bed calorimeter; R_{1}, rheostat for
controlling electric heaters in ingoing water in calorimeters; S_{8},
double-pole single-throw switch for connecting 110-v. current with
connections on table; S_{9}, double-pole single-throw switch for
connecting R_{1} with bed calorimeter.]
Of special interest are the electrical connections on the observer's
table itself. A diagrammatic representation of the observer's table with
its connections is shown in fig. 17. The heavy black outline gives in a
general way the outline of the table proper and thus shows a
diagrammatic distribution of the parts. The first of the electrical
measurements necessary during experiments is that of the
thermo-electric effect of the thermal junction systems installed on the
calorimeters. To aid in indicating what parts of the zinc wall need
cooling or heating, the thermal junction systems are, as has already
been described, separated into four sections on the chair calorimeter
and three sections on the bed calorimeter; in the first calorimeter, the
top, front, rear, and bottom; in the bed calorimeter, the top, sides,
and bottom.