In the early days of electric lighting a good many experiments were tried with threads of platinum, but without success. That metal remains unmelted at a very high temperature, but as a light-giver its quality is poor. Of late years investigators have turned to other metals, of high melting points, and with results so remarkable that we may expect some of them to be in general use in the near future. Tantalum, a rare and costly metal, has been found to give a candle-power with as little as two watts and, in specially favorable circumstances, with only 1.85 watts. Osmium, in the hands of Dr. Auer von Welsbach, reduces this figure to 1.5 watts. Dr. Hans Kuzel, of Baden, Austria, has employed filaments of tungsten in lamps which he claims demanded only one watt per candle. From among these new lamps it seems highly probable that as soon as methods of manufacture are settled and standardized the world will be given an electric light, in small units, much cheaper than ever before. [Illustration: Tantalum lamp.] [Illustration: Tungsten lamp of Dr. Hans Kuzel.] New Arc Lamps. For large spaces indoors and for out of doors the arc-lamp maintains its popularity in much the form originally devised by Mr. Charles F. Brush of Cleveland. But, as in the case of the incandescent bulb, many a rival is now disputing the field, so that supersedure may be close at hand. In what are known as flaming or luminous arcs the carbon pencils are impregnated with salts of the calcium group of elements, of extreme luminosity. In these lamps the electric arc itself is the chief source of light, instead of the glowing end of the positive carbon as in a common arc lamp. As the calcium salts volatilize into gases they provide a path of less resistance than air for the passage of the current, so that the electrodes may be drawn apart to a distance which may be as much as 2-1/2 inches. These lamps require free ventilation, so that they must be open. Their economy is extraordinary, a candle-power being afforded for .353 watt, as against 1.78 watts for an enclosed arc lamp, a five-fold gain in effectiveness. To renew the carbons, which waste rapidly, a new device provides fresh pencils, cartridge fashion, as required. Without this aid, trimming is often necessary, and this fact joined to the high cost of the carbons lessens the net gain in their use. On another line of experiment noteworthy results have been reached with metallic oxides. Magnetite, an oxide of iron, has developed a candle-power with but one half of one watt. Ferro-titanium, a compound of iron and titanium, has given a candle-power with only one third of a watt, and it is expected that still higher efficiencies will soon be attained with this wonderful compound. [Illustration: Hewitt mercury-vapor lamp.] Hewitt Mercury-Vapor Lamp.