The applications of the arc light have been brilliant beyond the dreams of the most sanguine inventor. In the illustrations number 44, 45 and 46, is shown a gigantic electric light beacon manufactured by Henry Lepaute, of Paris, and first exhibited in this country at the Chicago World’s Fair, in 1893. It consists of two great lenses, each nine feet in diameter, between which, in their focus, is placed a 9,000 candle power arc light. The great lantern, Fig. 45, is carried by a vertical shaft, which terminates at its lower end in a hollow drum, which latter floats in a bath of mercury. Although the weight is estimated at several tons, so sensitive is its poise on the mercury that the enormous lantern may be easily rotated by the pressure of one’s finger. Each lens consists of concentric segments, see Fig. 46, 190 in number, surrounding a central disk, which together cause the rays to issue in parallel lines. The nine-foot beam of light thus projected is of 90,000,000 candle power, and if placed at a sufficient altitude to avoid the curvature of the earth’s surface, its light would be visible at the range of 146.9 nautical miles. [Illustration: FIG. 45.--NINETY MILLION CANDLE POWER BIVALVE LENS.] [Illustration: FIG. 46.--FRONT VIEW OF LENS.] Better known to the patrons of our excursion boats and the visitors to our splendid battleships, are the electric search lights. The greatest example of all search lights, however, is not to be found on the sea, but in the picturesque altitudes of the Sierra Madres in Southern California. At the summit of Mount Lowe, in the neighborhood of Pasadena, is the largest search light in the world, shown in illustration, Fig. 48. It is of 3,000,000 candle power, stands eleven feet high, and its total weight is 6,000 pounds. Its light may be seen for 150 miles out on the ocean, and as its powerful beam is thrown from mountain top to mountain top hundreds of miles apart, it adds the illumination of art to the sublimity of nature, and seems a fitting jewel to this lofty crown of Mother Earth. [Illustration: FIG. 47.--SEARCH LIGHT WITH MACHINE GUN REPELLING NIGHT ATTACK OF TORPEDO BOAT.] [Illustration: FIG. 48.--SEARCH LIGHT ON MOUNT LOWE, CALIFORNIA.] Brilliant as is the arc lamp, far more in evidence is the incandescent lamp. The little glass bulb with its tiny thread of light we find everywhere. Popular opinion and the decision of the courts accord this invention to Thomas A. Edison. The evolution of the incandescent lamp is, however, interesting, and may be briefly sketched as follows: [Illustration: FIG. 49.--FIRST INCANDESCENT LAMP, BY PROFESSOR GROVE, 1840.] [Illustration: FIG. 50.--STARR-KING LAMP.]