Fig. 1,037.—Betts' clock mechanism for operating electric monogram time flasher. The secondary mechanism consists of a three cylinder flasher and is controlled by a master clock which transmits an electric impulse through a relay switch one each minute. This flashes the time in figures on the monogram, viz.: 11.45, 11.46, 11.47, 11.48, etc. The first monogram to the left consists simply of a vertical row of lights representing the figure one. Each of the other monograms of metal compartments so arranged that any figure may be produced by lighting the proper combination of lamps.
Talking Signs.—This type of electric sign automatically flashes out in brilliant letters, different phrases or announcements. These are flashed out repeatedly and continuously during the operation of the sign and the changes follow each other without intermission of darkness.
Fig. 1,038.—Two way thermal flasher. The moving portion consists of a rocking arm A pivoted at p, and carrying two sealed bulbs, B, B', whose bottoms are united by the tube T. Inside there is sufficient mercury M to fill T and the bottoms of the bulbs, the remainder containing air. At each end of A is fixed an insulating block I, I', carrying two contact prongs P and P', which are connected together at the top through heater wires H, H' sealed in the bulbs B and B' respectively. MC, MC' are pairs of mercury cups, the further one of each pair whose stud is marked +, being connected together to the positive pole of the circuit, while the front ones are joined up to the respective groups of lamps. The action is as follows: If the apparatus be in the position illustrated, when the circuit is closed at the time P is down, lamp group No. 1 will light up, the current passing through H on its way. The air in B consequently expands, and gradually forces the mercury down in B, along T, and up in B'. The arm A will gradually become horizontal, and will then overbalance, P being withdrawn from MC, and P' dipped into MC'. Lamp group No. 1 will consequently be extinguished and lamp group No. 2 lighted; H will cool down, and H' will warm up. Thus, in due course, A will be tilted the other way again.
The talking sign consists of any desired number of monograms or units, in each of which any letter or figure can be formed by lighting certain combinations of incandescent lamps. A unit is shown in [fig. 1,032]. The lamps are controlled by a simple mechanical arrangement operated by a small motor. Any reading matter can be flashed by properly setting the mechanism.
The flashing of the letters or numerals in the monogram is controlled by commutators, one commutator being required for each monogram, except for a double faced sign where the corresponding monogram on each side is controlled by the same commutator.
CHAPTER XLIII
LIGHTNING PROTECTION
A lightning arrester is an apparatus designed to provide a path by which lightning disturbances or other static discharges may pass to earth. Lightning arresters may be divided into three classes, according as their action depends upon the effects of: