ELECTRO-MAGNETIC INSTRUMENTS. 



Fig. 431. 



17 



(Fig. 431, as above.) This cut represents the same in- 

 strument, mounted on a mahogany base, having a graduated 

 circle for estimating the deviations of the needle. 



Price, $3.50. 



Fig. 432. 



Galvanometer. One of the simplest forms of the instru- 

 ment is that represented in Fig. 432, in which a common 

 compass-needle is suspended on a pivot proceeding from a 

 wooden stand, and enclosed by a great number of turns of 

 wire, bent into the shape of a vertical parallelogram, and 

 the two ends of which terminate, as usual, in small metallic 

 cups, for the purpose of establishing connexions with any 

 galvanic combination of which we are desirous to ascertain 

 and measure the electrical state. A graduated circle, hav- 

 ing a dark line across it, coinciding with the plane of the 

 wires, is fixed to the pivot, immediately under the needle, 

 to estimate its deviations in either direction from that plane. 



Price $3.50. 



2* 



