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.
An ordinary pocket flash lamp is prepared in the following manner: A brass spring, as shown in the sketch, is bound tightly to the flash lamp with a cord, and two wires, one at each end, are twisted around the lamp's body, forming two loops at the top. The kite string is run through the loops and over the spring. The lamp is then placed near the kite. The ordinary pull on the kite string does not close the spring, but a sharp jerk will pull the string in contact with the push button and its slight pressure causes an instant flash of the light. By this method words may be spelled out in the telegraph code. - Contributed by Joe V. Romig, Allentown, Pa.
Ill: The Flash of the Light on the String may be Read as Far as It can be Seen