This system of connecting the thermal junctions in different sections to the galvanometer makes possible a more accurate control of the temperatures in the various parts, and while the algebraic sum of the temperature differences of the parts may equal zero, it is conceivable that there may be a condition in the calorimeter when there is a considerable amount of heat passing out through the top, for example, compensated exactly by the heat which passes in at the bottom, and while with the top section there would be a large plus deflection on the galvanometer, thus indicating that the air around the zinc wall was too cold and that heat was passing out, there would be a corresponding minus deflection on the bottom section, indicating the reverse conditions. The two may exactly balance each other, but it has been found advantageous to consider each section as a unit by itself and to attempt delicate temperature control of each individual unit. This has been made possible by the electrical connections, as shown on the diagram. 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 R_{2}. 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 S_{5}. The other side of the switch S_{5} connects directly with the point on the middle of switch S_{10}, 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 R_{2}, are connected with the binding posts on S_{10}, 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 R_{2}, 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 R_{1}. This R_{1} 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 S_{9}. 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 R_{1} suffices for both. WHEATSTONE BRIDGES.