Articles which have been electroplated must be buffed to give them a bright polish. ELECTRIC CURRENT GENERATED BY HEAT. If the point of contact between two dissimilar metals is heated, a current of electricity will be generated. This principle was discovered nearly one hundred years ago by a scientist named Seebeck, and has resulted in many attempts on the part of inventors to utilize the heat of the sun’s rays in producing electricity. [Illustration: FIG. 187.—Generating Electric Current by Heat.] An interesting experiment illustrating the production of electricity by heat can be easily performed with very simple apparatus. An alcohol lamp, candle or source of heat, a piece of copper, a steel needle and a galvanometer or a telephone receiver are all that are necessary. The galvanometer or the telephone receiver, whichever is used, is for the purpose of detecting the electric current. Connect the needle and the piece of copper, which should preferably be a small sheet, to the galvanometer or telephone receiver. Hold the copper sheet over the flame of the alcohol lamp until it is quite hot and then touch the hottest portion with the point of the needle. Enough current will be generated to produce a click In the telephone receiver or to cause the galvanometer needle to move. The needle should be pressed against the copper tightly enough so that the point cuts through the scale or oxide on the surface and makes a good electrical contact with the metal underneath. Various devices for the production of electricity consisting of a large number of strips of dissimilar metals in contact with one another and arranged so that they can be easily heated have been invented. They are called "thermopiles." A HANDY LIGHT. Figure 188 shows a simple and handy form of light which utilizes the current from a home made primary cell. It consists of a glass fruit jar, fitted with a tight wooden top. A miniature porcelain socket and a 1.5 volt tungsten lamp are mounted on top. The battery is arranged so that the zinc element can be drawn up out of the solution when the light is not in use and any waste thereby prevented. The zinc electrode consists of a strip of that metal fastened onto the lower end of a brass rod by means of two threaded nuts. The upper end of the rod passes through a small metal collar on the top of the cover, provided with a thumb-screw so that when the electrode is lifted up out of the solution it may be clamped firmly in that position. The zinc strip should not be so long that it will not clear the solution when raised up if the jar is about half filled. [Illustration: FIG. 188.—A Handy Light.] The positive electrode is a battery carbon mounted on the lower end of a brass rod. The brass rod in this case is not movable because the carbon can remain in the solution indefinitely without any waste.