023 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



a distance, and wounded or killed the persons who might be in the 

 path of the electric fluid. Each station, has, in consequence, been 

 provided with a very simple little apparatus, for the purpose of draw- 

 ing off the electricity of the storm to the ground, and of saving the 

 instruments and the clerks at the same time. These lightning-con- 

 ductors are various in principle and form. We will describe a few 

 of those most in use. 



Breguet's lightning-conductor, represented in Fig. 410, is of great 

 simplicity. It consists essentially of two toothed metallic plates 

 whose teeth are opposite each other ; of a tube inclosing a very 

 fine iron wire, connecting electrically the screws a and b; and of 



FIG. 410. Breguet's lightning-conductor. 



FIG. 411. Lightning-conductor on the French 

 telegraphic lines. 



a commutator, p. When the handle of this last occupies the position 

 shown in the figure, the current from the line passes from L to F, and 

 thence into the apparatus of the station. The electricity of the 

 battery is not of sufficient tension to cross by the points of the plates, 

 and continues its ordinary course, but the atmospheric electricity, on 

 the contrary, is able to do so, and passes from the points by the wire 

 T to the ground. If the storm is violent, this way of escape may be 

 insufficient, and the electricity may pass through the wire, and 

 heat and even fuse it. But in the last event, the communication with 



