Robert Gibson Griswold.

The electric semaphore is an electrically operated signal which denotes, in the case of a block system, a clear or otherwise block, or section of track. The fact is indicated by the position of the semaphore arm with regard to the pole. When it hangs down at an angle of about 30° the block beyond, and over which it has control, is supposed to be clear; if the arm stands at an angle of 90° as shown in the cut, the block is already occupied by another train or car as the case may be.

In order that the semaphore may properly perform its function it is necessary that an electrical connection be made such that the presence of a car upon that particular brook controlled by the signal will cause the solenoid to draw the arm into a horizontal position. In the present case this is accomplished by insulating the two rails from each other in every section of track where this signal is used. A wire is then connected between each rail and one of the solenoid terminals, one of these wires having a small battery connected in series with it so that the current when passing through the rails, across from one to the other through the car axle, and through the solenoid will cause the signal to act. This semaphore cannot well be worked from the general current on account of the difficulty in winding the coil so that a small current will make it sufficiently powerful, and the interposition of the proper resistance to keep the power current from operating the signal at other than the proper time.

The movable arm is mounted on the side of a pole about twelve or fifteen inches high as shown. It is lightly pivoted on a small wire nail, the motion being limited by two similar nails being driven in above and below the arm. The arm is best cut from aluminum and one end provided with a circular opening into which a piece of red glass is cemented with pitch. The weight of this glass should not be so great as to overbalance the longer end, but the latter should be sufficiently heavy to cause the arm to fall when the current is shut off, drawing the iron core out of the coil as it falls. The vane or longer portion should be painted red with a white strip across the outer end, or this stripe may be made by leaving.the metal unpainted.

The solenoid is simply a coil of wire wrapped around a small tube of paper. This coil acts as a magnet when the current is passing around it, and will draw a piece of iron into the tube with considerable force. Make the spool either of wood turned out on a lathe, or a stiff paper provided with two flanges and given two coats of shellac. When quite dry place spool on a small wood mandrel and proceed to wind it full of No. 25 B. & S. single cotton covered magnet wire. The spool should be about 1 1/4" long x about 3/8" in diameter, the hole being 3/16" in diameter. Give the finished winding two or three coats of shellac and place in an oven to dry, after which it will be found very hard and firm. Allow the ends of the wire to extend from thecoil at least 15".

The core for this solenoid is made of a ten-penny wire nail which is about 1/8" in diameter, and slightly shorter than the coil. One end is fastened to a wire which runs up as shown and hooks fast to the arm about 1/4" from the pivot. The iron core should move easily in the spool, and a small nail or pin driven into the pole just above the spool will serve to prevent its touching the tube while moving. The solenoid may also be located at the base of pole, enclosing it in a box frame with sloping roof to represent a signal box

A small tin lamp box is made and attached to the pole, inside of which is secured a small pea electric lamp, the wire from which pass down the side of the pole or through a hole drilled through the centre of the pole, the wires entering a hole drilled at right angles as shown for the solenoid wires. This makes a very neat job. The lamp box is provided on the side with a circular opening which is just the size of the glass in the semaphore arm. When the arm falls the red glass uncovers this opening and the white light shows instead. The light should be connected to separate battery, as in fact they all should, so that shutting down of the power current will not affect them.

This signal may also be used to indicate the condition of a switch on the main line; one position, generally the horizontal, indicating that a switch is open ; the fallen position indicating that the track is clear and the switch closed.