CONNECTIONS TO THERMAL-JUNCTION SYSTEMS.
Since heretofore it has been deemed unwise to attempt to use both calorimeters at the same time, the electrical connections are so made that, by means of electrical switches, either calorimeter can be connected to the apparatus on the table.
The thermal-junction measurements are made by a semicircular switch S7. The various points, i, ii, iii, iv, etc., are connected with the different thermal-junction systems. Thus, by following the wiring diagram, it can be seen that the connections with i run to the different binding-posts of the switch S10, which as a matter of fact is placed beneath the table. This switch S10 has three rows of binding-posts. The center row connects directly with the apparatus on the observer's table, the outer rows connect with either the chair calorimeter or the bed calorimeter. The points marked a, b, d, e, f, etc., connect with the bed calorimeter and A, B, D, etc., connect with the chair calorimeter. Thus, by connecting the points g and i with the two binding-posts opposite them on the switch S10, it can be seen that this connection leads directly to the point i on the switch S7, and as a matter of fact this gives direct connection with the galvanometer through the key on S7, thus connecting the thermal-junction system on one section of the bed calorimeter between g and i directly with the galvanometer. Similar connections from the other points can readily be followed from the diagram. The points on the switch S7 indicated as i, ii, iii, iv, correspond respectively to the thermal-junction systems on the top, rear, front, and bottom of the chair calorimeter.
By following the wiring diagram of the point v, it will be seen that this will include the connections with the thermal junctions connected in series and thus give a sum total of the electromotive forces in the thermal junctions. The point vi is connected with the thermal-junction system in the air system, indicating the differences in temperature between the ingoing and outgoing air. It will be noted that there are four sections in the chair calorimeter, while in the bed calorimeter there are but three, and hence a special switch S3 is installed to insure proper connections when the bed calorimeter is in use.
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.