Fig. 51
Fig. 52
22. Volt meter.—The volt meter measures the pressure of an electric current. The volt meter which we examined looked outside like our ammeter, and when we removed the face it appeared inside like an ammeter. There was the steel magnet of horseshoe shape to furnish a field ([Fig. 51]), and there was an electro-magnet poised between its poles for an armature. The armature in the volt meter, however, had wound upon it finer wire and more of it than was the case in the ammeter. There was no shunt wire in the volt meter as there was in the ammeter. We connected in series a fluid cell (to be described later), the ammeter, and the volt meter ([Fig. 52]). The ammeter shunt was removed so that all the current went through its armature. The volt meter needle went to one which was two thirds of the scale ([Fig. 53]), and the ammeter needle indicated .016. That is, this particular cell can push sixteen thousandths of an ampere through the resistance of this volt meter, and .016 ampere passing through the armature of this volt meter will magnetize it sufficiently to move it against its spring, say sixty degrees.
Fig. 53
