CHAP, 



. viii.J 



THE ELECTRIC LIGHT. 



697 



on a handle. This separation, by the resulting diminution of force 

 in the armature of the electro-magnet, gives rise to an induced 

 current in the wires of the coil, and also to an extra current whose 

 intensity is added to that of the induced current. It is chiefly the 

 power of the extra current which is used for the production of 

 the spark, and M. Breguet has invented an arrangement which 

 enables this power to be used at the precise moment it has attained 

 its maximum value. 



For this purpose a spring band, in contact with a screw, does not 

 leave it till the Cessation of motion of the piece of soft iron. Now 



FIG. 451. Magnetic exploder for blasting mines Breguet's system. 



the wires of the electro-magnet end, one in the screw, and the other in 

 the spring, so that as long as the contact lasts the circuit remains closed 

 upon itself, and the extra current arrives at its maximum when the 

 contact ceases, and at that moment the discharge is made across the 

 circuit ending in the mine. 



To avoid accidents when the apparatus is put into communication 

 with several mines, a bolt stops the motion of the handle and it 

 cannot be worked, until, all being ready, the bolt is drawn. The signal 

 may then be given without fear. 



The apparatus which we have just described may be, and in fact 



