658 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



watch and said, ' It is now ten seconds to twelve. At the order of 

 the clock of my laboratory at Paris my divider begins to move. The 

 diamond traces five marks in the air to put itself in train and to 

 warm the oil at the junctions and supports. It makes five useless 

 marks on a plate of glass to show that it bites on it. It advances to 

 the place where it has to begin its work ; it traces its definite lines, the 

 shortest for thousandth parts of millimetres longer ones every five, 

 and a little longer still every ten. It traces five hundred of these. 

 It has finished its task, and remains in its place with its point in 

 the air ready to recommence. In its turn, the clock indicates thirty 

 seconds after twelve, so that when he returns to Paris the master 



Fid. 429. Chenot's electric sorter. 



may assure himself that his electric slave has scrupulously obeyed 

 him.'" 



We now see that it is not power, but regularity and velocity that 

 we may obtain from electricity, considered as a prime mover. It is 

 this that has been required in telegraphy, and almost all the appli- 

 cations to which we have referred. We will give a few more 

 examples. 



The energy which excites an electro-magnet, whenever a current 

 is thrown into the wires of its bobbins, had been used in that 

 metallurgical operation which consists in sifting certain minerals 

 so as to separate the parts which are richest in metal from compounds 

 of another kind. We can do this with those metallic oxides which 

 become magnetic, by roasting or reduction. A machine is made 



