A button of compressed lampblack is placed in series with a battery and
galvanometer. A strip of some substance, affected in its length either
by heat or by moisture, is held pressing against the button. A slight
change in length of the strip varies the resistance of the button and
hence affects the galvanometer. In this way exceedingly slight changes
in heat or moisture may be indicated.
For heat indications vulcanite may be used. The heat of the hand held
near it is enough to affect the galvanometer. For moisture a slip of
gelatine is used. The moisture of a damp slip of paper two or three
inches distant is sufficient to affect the galvanometer.
In the cut, Fig. 2, shows the general distribution of the apparatus in
circuit with a battery and galvanometer. C is the base of the apparatus,
from which the standard, B, with adjusting screw, H, rises. The strip of
vulcanite is held between I and G. Within D is the carbon button (F in
Fig. 3) pressed between G and E; A is a standard to carry the parts last
described. In Fig. I it is shown as part of a Wheatstone bridge, a, b
and c being resistance coils; l the tasimeter, and g the galvanometer.
If a balance is secured, any variation in the resistance of the
tasimeter will disturb the galvanometer.
Synonym--Tasimeter.
Fig. 243. MICROTASIMETER.