This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
The material required to construct a telegraph sounder, like the one shown in the sketch, consists of two binding posts, magnets, a piece of sheet metal, and a rubber band. These are arranged as shown, on a wood base or, better still, on a metal box. In using a metal-box base, be sure to insulate the connections at the magnet coils and binding posts.
This instrument will be found by those studying the telegraph codes to give good results, equal to any of the expensive outfits sold for this purpose. - Contributed by Chas. J. La Prille, Flushing, N. Y.
Ill: An Inexpensive and Homemade Sounder for Use in Learning the Telegraph Codes