Three snakes would cost about 25 per cent. less for flasher and wiring than for two snakes. The smaller the number of snakes travelling around the border at one time, the greater the expense of wiring and flasher.
Fig. 1,029.—Thermo flasher. It consists of two metal strips, one of brass and the other of iron, about 5"x ½" x 1/32" each. The brass strip is provided with a winding of fine wire over asbestos and the two strips are connected to the base as shown. One terminal of the winding is connected to J, and the other end to M. At the end of the strips is a small contact screw N with locknut O, and below is a contact plate L, fastened to the base and terminal post R. The flasher is connected at P and R in series with the lamp it is to flash, and N adjusted so that it clears the plate about 1/32 inch when there is no current flowing in the winding. When the switch is turned on there will be a current through the lamp and winding in series. The brass strip will be heated more than the iron and it will expand more, thus forcing the point of the screw N down upon the brass plate, which will result in the winding about the brass strip being shorted and the full voltage will be impressed upon the lamp, and it will burn at normal candle power. When the coil is shorted there will of course be no current in its winding and the brass strip will cool down, the screw N will finally be drawn away from contact with the brass plate, and the winding again connected in series with the lamp. The lamp will apparently go out when the winding is in series with it, as the total resistance of the lamp and winding combined will not permit sufficient current to pass through the lamp to make its filament glow. The time the lamp is on and off may be varied to a certain extent by adjusting the screw N.
Ques. How many snakes should there be for best effect?
Ans. Two is considered best. Three may be used on some signs, but more than four would, in most cases, so crowd them as to spoil the effect entirely.
Thermo Flashers.—These flashers work on the thermo or heat expansion principle, that is, the movement of the contact points of the flasher necessary to open and close the circuit is obtained automatically by the alternate heating and cooling of the metal of the flasher, which causes it to expand and contract.
Fig. 1,030.—Thermal flasher. This simple flasher consists of a brass strip fixed at each end to a porcelain base and slightly arched upwards. The amount of this arching, however, is much less than is shown in the figure. The center of the strip carries a platinum contact on its upper surface, and opposite this is a platinum tipped contact screw which is carried in a brass angle piece fixed to the base. One terminal is fitted on one end of the strip, and the other is connected, through the angle piece, with the contact screw. The strip is wound from end to end with an insulated resistance wire, one end of this being soldered to the strip, and the other connected to the right hand terminal. When this device is switched into circuit with the lamps, the current first flows through the resistance, which cuts it down so much that the lamps are not visibly affected. The heat generated in the resistance causes the strip to curve still more, till at length contact is made, the resistance short circuited, and the lamps lighted.