pounds of dynamite and 700,000 kilos. of illuminating oil. The problem of keeping the temperature and atmosphere of the tunnel within a limit involving perfect safety to persons passing through it, proved one of the most difficult encountered. It was satisfactorily solved by the establishment of immense steam-pumping machines, which constantly throw in an ample supply of fresh air, and maintain a temperature never rising above 20° Celsius or 68° Fahrenheit. There is at present being projected, by the Italian and Swiss governments, the Simplon tunnel, to pierce the Alps about midway between Mont Cenis and St. Gothard, which will be one kilometre longer than the St. Gothard,--that is, sixteen kilometres, or about ten miles in length. In practical engineering the Swiss may challenge rivalry with any other nation. The suspension bridge at Freiburg, constructed in 1834, at that time had the largest single curve of any bridge in the world, being nine hundred feet in length, and one hundred and eighty high. One of the most daring feats of modern engineering is the cog-wheel railway up to Pilatus-culm, on the Lake of Luzern, six thousand seven hundred and twenty-four feet high. The road-bed is of solid masonry faced with granite blocks. Streams and gorges are traversed by means of stone bridges. There are seven tunnels from thirty to three hundred feet in length. The rack-rail, midway between and somewhat higher than the tracks, is of wrought steel, and has a double row of vertical cogs milled out of solid steel bars. The locomotive and car containing thirty-two seats form one train, with two movable axles and four cog-wheels gripping the cogs, and which, on downward trips, can be controlled by vigorous automatic brakes. The speed of the locomotive is two hundred feet per minute. The road has an average gradient of about one foot in every two. Another piece of skilful engineering and of much scientific interest is the new electric mountain railway up the Burgenstock, also on the Lake of Luzern, it being the first application of this powerful agent to a mountain railway. The primary source of the motive power is three miles away, where an immense water-wheel of one hundred and fifty horse-power has been erected. This works two dynamoes, each of thirty horse-power. The electricity thus generated is transmitted for three miles across the valley, by means of insulated copper wires, to another pair of dynamoes, the negatives of the first, placed in a station at the head of the railway. Here the electric force is converted into mechanical power by the ordinary connection of leather belts, gearing the dynamoes, to two large driving-wheels of nine feet diameter. Then by shafting and cogs the power is carried on to an immense wheel of sixteen feet diameter, and around this passes a wire rope with each end connected to the cars. One man only is required to control the motion of the cars. The whole apparatus