inally adjust 0 after S' is fixed and _t_ is a permanent shunt
across the thermometer T_{1} to make the temperature coefficient of
T_{1} equal to that of T_{2}.

The apparatus can be used for measuring temperature differences from 0 deg.
to 4 deg. or from 0 deg. to 8 deg. When on the 0 deg. to 8 deg. range, the
shunt S is open-circuited and the shunt S' alone used. The value of S,
then, is predetermined so as to affect the value of the wire J and thus
halve its influence in maintaining the balance. Similarly, when the lower
range, _i. e._, from 0 deg. to 4 deg., is used, the resistance _r_ is
employed, and when the higher range is used another value to _r_ must be
given by using a plug resistance-box, in the use of which the resistance
_r_ is doubled.

The resistance S'' and S_{1} are combined in a slide-wire resistance-box
and are used to change the value of the whole apparatus when there are
marked changes in the position of the thermometric scale. Thus, if the
ingoing water is at 2 deg. C. and the outcoming water at 5 deg. C. in one
instance, and in another instance the ingoing water is 13 deg. and the
outgoing water is 15 deg., a slight alteration in the value of S_{1}, and
also of S', is necessary in order to have the apparatus draw a curve to
represent truly the temperature differences. These slight alterations
are determined beforehand by careful tests and the exact value of the
resistances in S' and in S_{1} are permanently recorded for subsequent
use.

THE GALVANOMETER.

The galvanometer is of the Deprez-d'Arsonval type and has a particularly
powerful magnetic field, in which a double coil swings suspended similar
to the marine galvanometer coils. This coil is protected from vibrations
by an anti-vibration tube A, fig. 20, and carries a pointer P which acts
to select the direction of movement of the recording apparatus, the
movable contact point _q_, fig. 19. In front of this galvanometer coil
and inclosed in the same air-tight metal case is the plunger contact Pl,
fig. 21. The galvanometer pointer P swings freely below the silver
contacts S_{1} and S_{2}, just clearing the ivory insulator _i_. The
magnet plunger makes a contact depending upon the adjustment of a clock
at intervals of 2 seconds. So long as both galvanometer coils are
influenced by exactly the same strength of current, the pointer will
stand in line with and immediately below _i_ and no current passes
through the recording apparatus. Any d