214 THE ELECTRIC TELEGRAPH. 



and ending in terminal screws. A tap is also inserted in 

 the copper ring, through which the air is pumped out. The 

 ring is supported by a metal plate at the back, connected to 

 earth, and by which the lightning discharger is fixed against 

 the outside of the building. 



The foregoing are some of the best arrangements invented 

 as yet for protecting the apparatus from the effects of 

 atmospheric electricity. They all, in a more or less com- 

 plete degree, fulfil their purpose, but none with entire 

 certainty, as we from time to time observe in the damaging 

 effects of a thunder-storm to the apparatus at stations which 

 are supplied with dischargers of the best constructions. On 

 other occasions, however, the dischargers do their duty in 

 saving the stations and apparatus from serious damage. 

 Such a case was mentioned in the Electrician in a letter 

 from one of the officials of the Levant submarine tele- 

 graph line. The writer says that a heavy thunderstorm, 

 passing over the Island of Metelin, completely destroyed 

 eight poles, and was only prevented from going into the 

 cable by a plate lightning discharger, the iron plates of 

 which were fused together. 



