ON THE CONSERVATION OF FORCE. 357 



of the poles of the horse-shoe magnet, and in these coils 

 electrical currents are produced, which can be led from 

 the points a and b. If the ends of these wires are con- 

 nected with the apparatus for decomposing water we 

 obtain hydrogen and oxygen, though in far smaller quan- 

 tity than by the aid of the battery which we used before. 

 But this process is interesting, for the mechanical force 

 of the arm which turns the wheel produces the work which 

 is required for separating the combined chemical ele- 

 ments. Just as the steam-engine changes chemical into 

 mechanical force, the magneto-electrical machine trans- 

 forms mechanical force into chemical. 



The application of electrical currents opens out a large 

 number of relations between the various natural forces. 

 We have decomposed water into its elements by such 

 currents, and should be able to decompose a large number 

 of other chemical compounds. On the other hand, in 

 ordinary galvanic batteries electrical currents are produced 

 by chemical forces. 



In all conductors through which electrical currents 

 pass they produce heat ; I stretch a thin platinum wire 

 between the ends n and p of the galvanic battery. Fig. 49 ; 

 it becomes ignited and melts. On the other hand, elec- 

 trical currents are produced by heat in what are called 

 thermo-electric elements. 



Iron which is brought near a spiral of copper wire, 

 traversed by an electrical current, becomes magnetic, 

 and then attracts other pieces of iron, or a suitably 

 placed steel magnet. We thus obtain mechanical actions 

 which meet with extended applications in the electrical 

 telegraph, for instance. Fig. 51 represents a Morse's 

 telegraph in one-third of the natural size. The essential 

 part is a horse-shoe shaped iron core, which stands in the 

 copper spirals b b. Just over the top of this is a small 

 steel magnet c c, which is attracted the moment an 



