OBSERVER'S TABLE.
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.
Fig. 17.—Diagram of wiring of observer's table. W1, W2, Wheatstone bridges for resistance thermometers; K1, K2, double contact keys for controlling Wheatstone circuits; S1, S2, S3, double-pole double-throw switches for changing from chair to bed calorimeter; S4, double-pole double-throw switch for changing from wall to air thermometers; G, galvanometer; R2, rheostat. 1, 2, 3, 4, 5, wires connecting with resistance-coils A B D E F and a b d e f; S2, 6-point switch for connecting thermal-junction circuits of either bed or chair calorimeter with galvanometer; S10, 10-point double-throw switch for changing heating circuits and thermal-junction circuits to either chair or bed calorimeter; R1, rheostat for controlling electric heaters in ingoing water in calorimeters; S8, double-pole single-throw switch for connecting 110-v. current with connections on table; S9, double-pole single-throw switch for connecting R1 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.