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 results obtained in a great many cases in trying to take pictures by flashlight are exceedingly unsatisfactory, as the expression on the faces of the people in the picture usually is strained or unnatural, due to the suspense in waiting for the flash. The following simple device avoids this difficulty because the flash is set off by means of electricity, so that the operator can control the flash from a distant point and thus be able to take the picture quite unawares to his subjects.
The construction of the device is As follows: Obtain a piece of rather heavy sheet iron, about 6 in. wide and 10 in. long. Bend this piece of iron into the form shown in the sketch, and fasten a wooden handle to it with a wood screw. Obtain a sheet of 1/8-in. sheet asbestos, the same size as the piece of sheet iron, and glue it to the inside surface of the curved piece of iron. It is best to fasten the four corners down by means of some small rivets with rather large washers under the heads next to the asbestos.
Now mount two pieces of sheet copper, 1/2 in. wide and (5 in. long, parallel with each other on the surface of the asbestos and 1 1/2 in. apart, so that their ends are even with the end of the piece of asbestos. These pieces of copper should be insulated from the piece of sheet iron, and there should be a small screw in one end of each and a small binding post mounted on the other end.
Procure a piece of lamp cord, 15 or 20 ft. in length. Fasten an ordinary plug to one end of this cord and the other end to the two binding posts.
Open one of the conductors in the cord at some point and introduce a single-pole switch, as shown in the sketch. Close the gap between the two pieces of copper by means of a piece of No. 32 gauge copper wire. Place the flashlight powder in position, but do not cover up the wire or have it in actual contact with the powder, and close the circuit. The operator may include himself in the picture by having a sufficiently long piece of lamp cord and the switch properly arranged.