Galvanoscopes and Galvanometers
In the first part of Chapter V it was explained that several turns of wire surrounding a compass-needle would cause the needle to move and show a deflection if a current of electricity were sent through the coil.
Such an instrument is called a galvanoscope and may be used for detecting very feeble currents. A galvanoscope becomes a galvanometer by providing it with a scale so that the deflection may be measured.
A galvanometer is really, in principle, an ammeter the scale of which has not been calibrated to read in amperes.
Fig. 110.—Simple Compass Galvanoscope.
A very simple galvanoscope may be made by winding fifty turns of No. 36 B. & S. gauge single-silk-covered wire around an ordinary pocket compass. The compass may be set in a block of wood, and the wood provided with binding-posts so that connections are easily made.
Another variety of the same instrument is shown in Figure 111.
Fig. 111.—Galvanoscope.