35S 



ON THE CONSERVATION OF FORCE. 



electrical current, arriving by the telegraph wire, traverses 

 the spirals b b. The magnet c c is rigidly fixed in the 

 lever d d, at the other end of which is a style ; this 

 makes a mark on a paper band, drawn by a clock-work, as 

 often and as long as cc is attracted by the magnetic 

 action of the electrical current. Conversely, by reversing 

 the magnetism in the iron core of the spirals b b, we 

 should obtain in them an electrical current just as we 



PIG. 61. 



have obtained such currents in the magneto-electrical 

 machine, Fig. 50 ; in the spirals of that machine there is 

 an iron core which, by being approached to the poles of 

 the large horse-shoe magnet, is sometimes magnetised in 

 one and sometimes in the other direction. 



I will not accumulate examples of such relations; 

 in subsequent lectures we shall come across them. Let 

 us review these examples once more, and recognise in 

 them the law which is common to all. 



