HISTORY AND PROGRESS. 



209 



attaching wires. To the screws/! and/ 2 are attached the up 

 and down line wires respectively ; to the sere ws/j and/ n the 

 wires leading to the apparatus i and n ; and, lastly, to the 

 screw g, the earth wire. 



The upper plates, b b, are kept in their places by small 

 knobs, c c, fixed to them, and by the buttons d d on the 



Fig. 114. 



earth-plate. In order to prevent metallic contact, these 

 buttons are covered with vulcanite, as are also the sides of 

 the earth-plate. 



The atmospheric electricity, on reaching the conductors 

 springs over to the earth-plate, and thus escapes the 

 apparatus. 



Another form of lightning discharger used on the Con- 

 tinent, especially on railway lines, is a modification of the 

 plate dischargers. It consists of three brass cylinders with 

 platinum faces, supported in an insulating frame. The line 

 wires are attached to the two end cylinders, between which 

 the receiving apparatus is inserted. The middle cylinder is 

 connected with earth. 



108. Breguefs Wire Lightning-guard. An excellent idea 

 was carried out by Breguet in the construction of his first 

 lightning discharger, in the employment of the power of the 

 spark to melt a fine wire, and of making the lightning itself cut 



