262 
THE TELEGRAPH, 
were not protected by lightning conductors. These act by 
conveying to the earth charges of atmospheric electricity which 
would otherwise injure the wires and the apparatus. 
The simplest method of doing this was invented by Stein- 
heil, and is in use in Belgium and Germany. As improved by 
Messrs. Siemens, it consists merely of two metallic plates fixed 
to a plank, and insulated from each other by pieces of ebonite 
at the four corners. A thin stratum of air is thus interposed 
between the plates, the upper one of which is part of the line 
current; while the lower one has an earth connection. Fig. 185 
Fig. 185. 
gives a perspective view of the arrangement, which is much 
used by submarine telegraph companies. Over the cast-iron 
earth-plate a , two other smaller plates of the same metal are 
placed, but without being in contact with it. These plates 
have screws for fixing the wires. At ff the underground 
wires are attached; at F, f', the submarine lines. The screw 
g is used for the earth wire. The upper plates are maintained 
in their position by pegs, c c, dd, covered with ebonite. The 
atmospheric electricity reaching the upper plate passes directly 
to the earth-plate. To facilitate the discharge, the plates are 
situated in directions at right angles to each other. 
Lightning will fuse very fine wires that offer much resistance 
to its passage, and it is precisely against this accident happen¬ 
ing to the fine wires of telegraph apparatus that these pre- 
