40 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



Fig. ^62. s j t y O f anv ac lj us t m ent of the size of the 



battery, the depth to which its plates are 

 immersed, &c. : h is a glass tube about 

 five inches in length, capped at each ex- 

 tremity ; this tube rests upon, but is not 

 fastened to, the base, g, as it may some- 

 times be desirable to attach the regulator 

 directly to the connector of the coil, by 

 the wire, f. The fixed copper wire, e a 

 f, bent to a right angle at a, passes 

 out close to the bottom of the cap, and 

 is fastened by the screw-connector, /. 

 The copper connecting-wire, c b d, passes 

 through a stuffing-box in the centre of 

 the upper cap, h (which unscrews in 

 order to introduce any convenient quan- 

 tity of water). The apparatus is interposed in the circuit 

 between one of the extremities of the coil and the person 

 about to receive the shock ; and, according as the points of 

 the wire d and e are approximated to, or separated from 

 one another, will be the strength or the gentleness of the 

 shock. Price, $4.00. 



Seebeck's Thermo- Electric Circuit. (Fig. 463, next page.) 

 An instrument which shows the electric effect produced 

 by heating dissimilar metals. It may be made of many 

 forms. That of a parallelogram is the most usual. The two 

 arms, A and B, are of one metal, for example, antimony ; the 

 other two arms, c and D, of a different metal, as bismuth 

 these are soldered at the corners. A stand supports the 

 whole, and bears besides a small magnet, the point of sus- 

 pension of which is about the centre of the parallelogram. 

 When the heat of a flame is thrown upon either of the corners 

 where the two metals meet, an electrical current is estab- 

 lished, and the magnet is diverted from its polar direction, 

 the north pole turning towards the east or west, according 

 to the position of the two metals, that is, according to the 

 course of the current. Price, $5,00. 



Thermo- Magnetic Rectangles. (Fig. 464, next page.) 

 These consist of slender wire frames, with four branches 

 suspended on a fine point attached to the upper part of the 

 rectangle, which is composed of pairs of dissimilar metals, 



