The average candlepower of standard lighting lamps has increased from 16, which prevailed during the period prior to 1905, to over 60. The average wattage has not varied much during the past twenty-odd years, the average lamp now consuming about 55 watts. This indicates that the public is utilizing the improvement in lamp efficiency by increased illumination. The present most popular lamp is the 40-watt size which represents 20 per cent of the total demand. Second in demand is the 25-watt at 18 per cent and third, the 50-watt at 15 per cent of the total in numbers. While the aggregate demand of all the gas-filled tungsten lamps is a little over 20 per cent in numbers, they represent, on account of their greater efficiency and wattage, over half the amount of total candlepower used. In the United States about 85 per cent of all lamps are for the 110-volt range. About 5 per cent for 220 volts, 2 per cent for street series lighting, 3 per cent for street railway and 5 per cent for trainlighting and miscellaneous classes of service. SELECTED BIBLIOGRAPHY ALGLAVE AND BOULARD, “The Electric Light,” translated by T. O’Connor Sloane, edited by C. M. Lungren, D. Appleton & Co., New York, 1884. BARHAM, G. BASIL, “The Development of the Incandescent Electric Lamp,” Scott Greenwood & Son, London, 1912. DREDGE, JAMES, “Electric Illumination,” 2 vols., John Wiley & Sons, New York, 1882. DURGIN, WILLIAM A., “Electricity--Its History and Development,” A. C. McClurg & Co., Chicago, 1912. DYER & MARTIN, “Edison, His Life and Inventions,” 2 vols., Harper & Bros., New York, 1910. GUILLEMIN, AMEDEE, “Electricity and Magnetism,” edited by Silvanus P. Thompson, McMillan & Co., London, 1891. HOUSTON, EDWIN J., “Electricity One Hundred Years ago and To-day,” The W. J. Johnston Co., New York, 1894. HOUSTON AND KENNELLY, “Electric Arc Lighting,” McGraw Publishing Co., New York, 1906. HUTCHINSON, ROLLIN W., JR., “High Efficiency Electrical Illuminants and Illumination,” John Wiley & Sons, New York, 1911. MAIER, JULIUS, “Arc and Glow Lamps,” Whittaker & Co., London, 1886. POPE, FRANKLIN LEONARD, “Evolution of the Electric Incandescent Lamp,” Boschen & Wefer, New York, 1894. SOLOMON, MAURICE, “Electric Lamps,” D. Van Nostrand Co., New York, 1908. Transcriber’s Notes Punctuation, hyphenation, and spelling were made consistent when a predominant preference was found in the original book; otherwise they were not changed. Simple typographical errors were corrected; unbalanced quotation marks were remedied when the change was obvious, and otherwise left unbalanced. Illustrations in this eBook have been positioned between paragraphs. In versions of this eBook that support hyperlinks, the page references in the List of Illustrations lead to the corresponding illustrations. “Allesandro Volta” was printed that way.