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.
It is often quite desirable to operate the shutter of a camera from a distance, especially in photographing birds and animals. The device shown in the accompanying sketch serves the above purpose very nicely, and its construction and operation are exceedingly simple. In brief, the operation is as follows: The switch A is mounted on the limb of a tree, in such a manner that it is not conspicuous, and connected in series with a magnet, B, and a battery by means of a piece of flexible conductor, such as lamp cord. The magnet B is energized when the switch is closed and attracts the iron armature C, which is mounted on an arm, pivoted at D. The lower end of this arm is in the form of a latch, which supports the rod E when it is raised to its upper position. The rod E when it is raised compresses the coiled spring F, which is held between the gauge G and the washer H mounted on the rod. A small coil spring holds the armature C away from the core of the magnet B. The lower end of the rod E is in the form of a piston operating in a wooden cylinder J. The rubber bulb at the end of the tube leading to the camera shutter is located in the lower end of the cylinder J. When the rod E is released by the latch K, it moves downward in the cylinder J, due to the action of the spring F, and compresses the bulb L, causing the shutter of the camera to be operated. A small handle, M, may be mounted on the rod to be used in raising it to the upper position. The component parts of this device may be mounted on a small wooden base by means of brass straps, and the terminals of the electric circuit connected to the binding posts N and O, as shown. The switch A may be dispensed with and a push button used in its place, as the operator may station himself several hundred feet away. It may be necessary to use a battery of more than one cell in such cases.
Ill: The Electromagnet Trips a Spring Plunger That Forces a Piston on the Camera Air Bulb