VOLTAIC ELECTRICITY, 



261 



FIG. 207. 



of two metals and one of the junctions be heated or 

 chilled, a current of electricity is produced. 



(a.) This may be 

 illustrated by the 

 apparatus shown 

 in Fig. 207. The 

 upper bar, mn, 

 having its ends 

 bent, is made of 

 copper ; the low- 

 er, op, is of bis- 

 muth. This rect- 

 angular frame is 

 to be placed in the 

 magnetic merid- 

 ian and a mag- 



netic needle placed within it. Upon heating one of the junctions a 

 current will be produced, the existence of which is satisfactorily 

 shown by the deflection of the needle as shown in the figure. The 

 junction may be chilled with a piece of ice or by placing upon it 

 some cotton wool moistened with ether. In this case a current, 

 opposite in direction to the first, will be produced ; the needle will 

 be turned the other way ( 390). (Appendix, L.) 



413. A Thermo-electric Pair. If a bar of anti- 

 mony, A, be soldered to a bar of bismuth, B, and the free 

 ends joined by a wire, as shown in 

 ^> we ey idently have a circuit 

 B equivalent to the one considered in 



the last paragraph. When the junc- 

 tion C is heated a current will pass from bismuth to anti- 

 mony across the junction, and from 

 antimony to bismuth through the 

 wire. 



(a) The arrangement is analogous to 

 the Voltaic element ( 374), the antimony 

 representing the plate and carrying 



B 



FIG. 209. 



