orological system; 2. The schistose rocks of the eastern half, in Vermont, are to a large extent similar to those of the western; 3. The rocks of the central mountain section in Vermont are, in its northern part, identical schists with those on the east and west sides of it; 4. The western border of the region in the Hudson River Valley has its folded or upturned Hudson River (Lower Silurian) slates overlaid unconformably by the Niagara and Lower Helderberg (Upper Silurian) beds; 5. The eastern border of the region in the Connecticut Valley at Bernardston, in Massachusetts, Vernon, in Vermont, and the adjoining part of New Hampshire, has Lower Helderberg beds overlying, unconformably, folded or upturned roofing-slates (similar to those on the western side), the Lower Silurian age of which is not improbable; and at Littleton, in New Hampshire, and on Lake Memphremagog, in northern Vermont, occur unconformable Upper Helderberg (Lower Devonian) beds with fossils; 6. A mountain-individual of folded rocks—which is defined as comprising all the elevations or results of upturning or flexure that were produced over a continuous region in one mountain-making process—is necessarily one of great magnitude. Professor Dana does not consider his theory as established, for a further study of the stratigraphy of the eastern part of the region is required for that, but he believes that the facts, which he reviews in detail, are strongly in its favor.
Gas and the Electric Light.—The question of the feasibility of substituting the electric light for gas is yet far from settlement. The competition will be finally decided by the consideration of the relative expense, regard being also given to the quality of the light afforded. Some experiments which have recently been made for increasing the illuminating power of gas have been attended with satisfactory results. The most effectual devices are those by which a more perfect combustion is secured. By concentrating a number of burners so arranged as to play upon each other, and by improved arrangements for regulating and directing the draught of air upon them, the amount of light has been tripled, and it has been made clearer and more fixed. Burners constructed with this object in view have been tried in London, and found to give a considerable increase of light at a less increase of expense. Other devices, produced by French inventors, promise well. The inventors of electric lights seek either to produce single lights to supplement the defective illumination given by ordinary lights, or to divide the light, so as to make it take the place of gas entirely. The apparatus devised by Messrs. Regnier and Werdemann and Mr. Edison, for the latter purpose, give an agreeable light; but that is only a part of the problem. The difficulty of securing an economical production and supply of electricity remains, and that equally whether we seek to distribute it so that each consumer shall use only what he needs, or to store it in reservoirs of force. Experiments which have been made upon the amount of light produced per horse-power of motive force give greatly varying results. The light of M. Mersanne, with the Lontin machine, is rated at 80 carcels; the Jablochkoff light, with the Gramme machine, at 38 carcels; and Mr. Edison's machine, with 10 of his carbon lamps, at 16 carcels. A comparative trial of the strength of the Jablochkoff and Mersanne lights and gas was made in the latter part of December at one of the railway-stations in Paris. Six of the Jablochkoff lights, ten compound intensive gas-burners, and four Mersanne lights, were used. The brilliancy of the gas-light was to the Mersanne light as 1 to 5·67, and to the Jablochkoff light as 1 to 1·927. On direct comparison, the brilliancy of the Jablochkoff was to the Mersanne as 1 to 3. Roughly, 6 Mersanne lights were equivalent to 1 8 Jablochkoffs and 34 gas-jets.
Composition and Uses of Celluloid.—Celluloid, which has come into extensive use in the arts, is a species of solidified collodion, produced by dissolving gun-cotton in camphor with the aid of heat and pressure. From a description of its composition and mode of manufacture by Dr. W. H. Wahl, we gather the following: The process of preparing gun-cotton is well known; by it the properties of the vegetable fiber are so changed that it becomes soluble in alcohol and ether, as in making collodion, camphor, and other substances. In the process invented by the brothers Hyatt, gun-
