RHEOSTAT FOR HEATING.
The rheostat for heating the air-spaces and the returning air-current about the zinc wall is placed on the observer's table and is indicated in the diagram as R2. There are five different sets of contact-points, marked 1, 2, 3, 4, and 5. One end of the rheostat is connected directly with the 110-volt circuit through the main switch S5. The other side of the switch S5 connects directly with the point on the middle of switch S10, and when this middle point is joined with either f and F, direct connection is insured between all the various heating-circuits on the calorimeter in use. The various numbered points on the rheostat R2, are connected with the binding posts on S10, and each can in turn be connected with a or A, b or B, etc. The heating of the top of the chair calorimeter is controlled by the point 5 on the rheostat R2, the rear by the point 4, the front by the point 3, and the bottom by the point 2. Point 1 is used for heating the air entering the calorimeter by means of an electric lamp placed in the air-pipe, as shown in fig. 25.
The warming of the electrical reheater placed in the water-circuit just before the water enters the calorimeter is done by an electrical current controlled by the resistance R1. This R1 is connected on one end directly with the 110-volt circuit and the current leaving it passes through the resistance inside the heater in the water-current. The two heaters, one for each calorimeter, are indicated on the diagram above and below the switch S9. The disposition of the switches is such as to make it possible to use alternately the reheaters on either the bed or the chair calorimeter, and the main resistance R1 suffices for both.