6 volts. 2 candle-power 6 volts. 4 candle-power 6 volts. 6 candle-power 6 volts. 8-10-12-16-20-24 candle-power [Illustration: Fig. 282.—Miniature Tungsten Battery Lamp.] To find the approximate amount of current drawn from a battery by a tungsten lamp, divide the candle-power by the voltage and the result will be the current in amperes. For example, a 6 v. 2 c. p. lamp will require, 2 divided by 6, or one-third of an ampere. Six-volt tungsten lamp giving a light greater than six candle-power are only used on storage batteries and are employed principally for automobile lighting. The filament of a tungsten lamp is much longer than that of a carbon lamp and is usually in the form of a spiral or helix, as shown in Figure 282. The bases of battery lamps, the base being the lower portion of the lamp, which is made of brass and fits into a socket or receptacle, are made in three different styles: _miniature_, _candelabra_, and _Ediswan_. [Illustration: Fig. 283.—Lamps fitted respectively with Miniature, Candelabra, and Ediswan Bases.] The miniature and candelabra bases have a threaded brass shell on the outside and a small brass contact-button on the bottom. They are similar except in respect to size. The miniature base is smaller than the candelabra. The Ediswan base is a plain brass shell having two pins on the side and two contacts on the bottom. This type of base is only used in this country on automobiles. The miniature and the candelabra bases are standard for battery lighting. The miniature base has many advantages over the candelabra for the young experimenter, and should be adopted in making any of the apparatus described in this chapter. These three bases are shown in Figure 283. [Illustration: Fig. 284.—Miniature Flat-Base Porcelain Receptacle.] In order to form a good electrical connection between the lamp and the power wires some sort of a receptacle or socket is necessary. The most common arrangement for this purpose is the miniature flat-base porcelain receptacle shown in Figure 284. This type of receptacle is used in places where it can be permanently fastened in position with two small screws. [Illustration: Fig. 285.—Weather-proof and Pin-Sockets.] The devices shown in Figure 285 are known respectively as a porcelain weather-proof socket and a pin-socket. Sockets similar to the weather-proof socket are also made of wood. The weather-proof sockets are used in places where the light is to be exposed out-of-doors, as for instance on a porch. The small metal parts are sealed in the porcelain and entirely protected. The pin-sockets and the wooden sockets are used principally on Christmas trees or in decorative outfits where lamps are hung in festoons. The flat-base receptacle, the pin-socket, and also the wooden socket will be found very useful in making the apparatus described farther on in this chapter.