isturbance of the electrical
equilibrium causes the pointer P to swing either toward S_{1} or S_{2},
thus completing the circuit at either the right hand or the left hand,
at intervals of 2 seconds. The movement of the pointer away from its
normal position exactly beneath _i_ to either S_{1} on the left hand or
S_{2} on the right, results from an inequality in the current flowing
through the two coils in the galvanometer. The difference in the two
currents passing through these coils is caused by a change in
temperatures of the two thermometers in the water circuit.

[Illustration: FIG. 20.--Diagram of galvanometer coil used in connection
with recording apparatus for resistance thermometers in the
water-circuit of bed calorimeter. A, anti-vibration tube; P, pointer.]

THE CREEPER.

The movement of the sliding-contact _q_, fig. 19, along the slide-wire
J, is produced by means of a special device called a creeper, consisting
of a piece of brass carefully fitted to a threaded steel rod some 30
centimeters long. The movement of this bar along this threaded rod
accomplishes two things. The bar is in contact with the slide-wire J
and therefore varies the position of the point _q_ and it also carries
with it a stylographic pen. The movements of this bar to the right or
the left are produced by an auxiliary electric current, the contact of
which is made by a plunger-plate forcing the pointer P against either
S_{1} or S_{2}. P makes the contact between Pl and either S_{1} or S_{2}
and sends a current through solenoids at either the right or the left of
the creeper. At intervals of every 2 seconds the plunger rises and
forces the pointer P against either S_{1}, _i_, or S_{2} above. The
movement of this plunger is controlled by a current from a 110-volt
circuit, the connections of which are shown in fig. 22. If the contact
is made at T, the current passes through 2,600 ohms, directly across the
110-volt circuit, and consequently there is no effective current flowing
through the plunger Pl. When the contact T is open, the current flows
through the plunger in series with 2,600 ohms resistance. T is opened
automatically at intervals of 2 seconds by the clock.

[Illustration: FIG. 21.--Diagram of wiring of circuits actuating plunger
and creeper.]

[Illustration: FIG. 22.--Diagram of wiring of complete 110-volt
circuit.]

The movement of the contact arm along the threaded rod is produced by
the action of either one of two sole