Fig. 311.—The Tin Reflector.
The pictures should be shown in a dark room and projected on a smooth white sheet. They are placed under the spring clips on the little door and the door closed. The movable tube is then slid back and forth until the picture on the screen becomes clear and distinct.
The lantern may be improved considerably by using tungsten lamps of 22 c. p. each in place of ordinary c. p. carbon filament lamps.
If four small feet, one at each corner, are attached to the bottom of the case, its appearance will be much improved.
Very large pictures will tend to appear a little blurred at the corners. This is due to the lens and cannot be easily remedied.
HOW TO REDUCE THE 110-v. CURRENT SO THAT IT MAY BE USED FOR EXPERIMENTING
Oftentimes it is desirable to operate small electrical devices from the 110-v. lighting or power circuits. Alternating current can be reduced to the proper voltage by means of a small step-down transformer, such as that described in Chapter XIII. Direct current may be reduced by means of a resistance. The most suitable form of resistance for the young experimenter to use is a "lamp bank."
A lamp bank consists of a number of lamps connected in parallel, and arranged so that any device may be connected in series with it.
The lamps are set in sockets of the type known as "flat-base porcelain receptacles," such as that shown in Figure 310, mounted in a row upon a board and connected as shown in Fig. 312.
The current from the power line enters through a switch and a fuse and then passes through the lamps before it reaches the device it is desired to operate. The switch is for the purpose of shutting the current on and off, while the fuse will "blow" in case too much current flows in the circuit.