The discovery of the X-Ray by Prof. Roentgen may be fairly considered one of the most wonderful scientific achievements of the century, and his first memoir in 1895 is so full, clear and exact, as to have left very little more to be said about it. It is to-day, as it was found by him in 1895, the same mysterious, unseen, but positive force, a species of electrical energy without a domicile, and needing no conductor, a form of light passing through closed doors, invisible itself, and yet lighting up certain substances with a halo of glory, and radically changing and decomposing others. Rivaling the sun in actinic power, and writing its autograph with an unseen hand, it is truly called the X-, or unknown, ray. CHAPTER XXVI. GAS LIGHTING. EARLY USE OF NATURAL GAS--COAL GAS INTRODUCED BY MURDOCH--WINSOR ORGANIZES FIRST GAS COMPANY IN 1804--MELVILLE IN UNITED STATES LIGHTS BEAVER-TAIL LIGHTHOUSE WITH GAS IN 1817--LOWE’S PROCESS OF MAKING WATER GAS--ACETYLENE GAS--CARBURETTED AIR--PINTSCH GAS--GAS METER--OTTO GAS ENGINE--THE WELSBACH BURNER. For many centuries the going down of the sun marked a cessation of man’s labors, and among his first efforts toward increasing his efficiency was the prolongation of his hours of vision by artificial illumination. Beginning with a shell for a lamp, a rush for a wick, and the fat of his game for oil, the first crude lamp was made, and while it shed but a feeble and flickering light, man ceased to go to sleep with the fowls and the beasts, and continued his labors and amusements into the night. For many centuries the lamp held its exclusive sway, and probably will ever find a useful place; but with the discovery of coal gas and its practical manufacture the nights of the Nineteenth Century have been made to represent illuminated illustrations of the world’s progress. Coal gas can hardly be claimed as an invention, however, for natural gas from the bowels of the earth had been observed and used in China from time immemorial. The holy fires of Baku on the shores of the Caspian and elsewhere were also thus supplied. The first steps toward its artificial production began in the latter part of the Seventeenth Century with Dr. Clayton. Bishop Watson, in 1750, and Lord Dundonald, in 1786, also experimented with combustible gas made from coal, but the man who more than any other contributed to its practical manufacture and introduction was Mr. Murdoch, of Redruth, Cornwall, England. In 1792 Murdoch erected a gas distilling apparatus, and lighted his house and offices by gas distributed through service pipes. In 1798 he so lighted the steam engine works of Boulton & Watt, at Soho, near Birmingham; and in 1802 made public illumination of the works by this means on the occasion of a public celebration. In 1801 Le Bon, of Paris, used a gas made from wood for lighting his house. In 1803-4 Frederick Albert Winsor lighted the Lyceum Theatre, took out a British patent No. 2,764, of 1804, for