MAGNETISM AND ELECTRICITY 



179 



the cylinder and the magnet poles. When the current is 

 sent through the coil it becomes a magnet which is acted 

 upon by the horseshoe magnet which 

 causes it to be deflected. The deflection 

 is measured on a scale which gives the 

 measurement of electricity. 



213. Ammeter. An ammeter (Fig. 

 80) is simply a commercial form of gal- 

 vanometer. It is constructed in the same 

 way, but only a small fraction of the 

 current to be measured passes through the 

 coil. The greater portion passes through 

 the shunt, which is located in one of the FIG. 79. D' Arson al 

 leads coming from the machine. The Galvanometer, 

 terminals on the shunt are connected to the terminals on the 

 ammeter by a pair of flexible leads about 10 ft. long. After 



the ammeter is made, it is tested 

 by operating one machine on a 

 certain number of lamps at exactly 

 110 volts and then throwing off 

 that machine and operating the 

 same number of lamps with an- 

 other machine. If readings on 

 the ammeter are the same, it is 

 correct. 



FIG. 80. Ammeter. 



214. Voltmeter. The volt- 

 meter is an instrument used to 

 determine the voltage of a circuit. It consists of a light, 

 rectangular coil of copper wire wound upon an aluminum 

 frame, pivoted in jeweled bearings, and capable of rotating 



