It consists of three pieces of sheet-brass about one-sixteenth of an inch thick, and shaped as shown by A, B, and C in Figure 100.
The metal pieces are mounted on a wooden block with a narrow space of about one-thirty-second of an inch separating them.
Fig. 100.—Home-made Lightning-Arrester.
The two outside pieces are each fitted with two binding-posts, and the center triangular-shaped piece is fitted with one post.
A hole about one-eighth of an inch in diameter is bored between each of the metal pieces.
Make a tapered metal pin which can be placed tightly in the holes, and will make contact between the metal pieces.
The two outside line wires of the telegraph circuit are connected to the outside metal pieces C and B. A is connected to the earth or ground.
In case of a lightning storm, if the wires become charged, the small space between the metal plates will permit the charge to jump across and pass harmlessly into the ground.
If complete protection is desired, it is merely necessary to insert the plug in one of the holes, and thus "ground" either wire or short-circuit both of them.