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
S_{7}. 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 S_{10}, which as a matter of fact is placed
beneath the table. This switch S_{10} 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 S_{10}, it can be seen
that this connection leads directly to the point I on the switch S_{7},
and as a matter of fact this gives direct connection with the
galvanometer through the key on S_{7}, 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 S_{7} 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 S_{3} 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.