The experimental line was laid down between Lanslebourg and the summit. It commenced at the height of 5,305 feet above sea level, and terminated at the elevation of 5,820 feet. Its length was two kilometres all but forty-four yards, or an English mile and a quarter. Gauge, 3 feet 7½ inches. Its mean gradient was 1 in 13, the maximum was 1 in 12; it had two curves of 44 yards each, and others, the most favourable of which was 125 yards. It will thus be seen that the line was constructed in a manner, both as regards gradients and curves, to subject the system to the severest tests. The experiments, which were conducted in the presence of commissioners from England, France, Italy, Austria and Russia, lasted from the end of February until the end of May 1865, and it is a remarkable fact that the adhesion was found during the period of snow better than could be expected in summer, for when snow was swept off the rails, it left them dry, and under favourable conditions; whereas, summer dust combined with moisture, would render them comparatively greasy and slippery. Captain Tyler, who was present at all the experiments on the part of the British Government, calls special attention to this curious fact in his report. Two engines were employed in the trials, the first that which had been used on the High-Peak Railway experiments, and the second an engine built specially for the service of the Mont Cenis Railway. This latter was the engine principally employed, No. 1 being chiefly used to supply the place of No. 2, when any trifling derangement in its machinery required attention. It is intended that No. 2 shall be used on the completion of the line over the pass, and it is the engine by which the trial trip was accomplished on the memorable 26th of August, 1867. When empty its weight is 13 tons, when loaded with coke and water 17 tons 2 cwt. The horizontal wheels and the machinery connected with them weigh 2¾ tons. The boiler is 8 feet 4 inches long, 3 feet 2 inches diameter, and contains 158 tubes of 1½ inches exterior diameter. Heating surface 600 feet. The cylinders, two in number, 15 inches diameter, with 16 inches stroke, act at one and the same time upon the two systems of wheels, four horizontal and four perpendicular. Each system of wheels consists of four coupled, diameter of each 2 feet 3 inches. The space between the centres of each pair of perpendicular wheels is 6 feet 10 inches, that between the horizontal wheels 2 feet 4 inches; maximum pressure of steam in the boiler 120 lbs. per square inch; effective pressure upon the piston 75 lbs. This engine was a great improvement upon its predecessor. With engine No. 1, Captain Tyler, R.E., from whose Report to the Board of Trade the foregoing particulars are taken, says that during the space of two days he descended and remounted the experimental line six times. The train behind it consisted of three waggons, with a total gross weight of 16 tons.