The difficulties encountered in the carrying out of these various geodetic operations can scarcely be exaggerated. It is true that nothing is more easy than to picket out a straight line on the ground, or to measure an angle correctly with a theodolite; but if we consider the aspect of the locality in which these operations had to be conducted, repeated over and over again, and tested in every available manner with the most minute accuracy, we shall be quite ready to accord our share of praise and admiration to the perseverance which successfully carried out the undertaking. In these regions, the sun, fogs, snow, and terrific winds succeed each other with truly marvellous rapidity, the distant points become obscured by clouds, perhaps at the very moment when an important sight is to be taken, causing most vexatious delays, and often necessitating a recommencement of the whole operation. These delays may in some cases extend for days, and even weeks. To these inconveniences add the necessity of mounting and descending daily with delicate instruments from three thousand to four thousand feet over rocks and rugged mountain-paths, the time occupied in sending from one point to another, and the difficulty of planting pickets on elevated positions often almost inaccessible. All these inconveniences considered, and we must admit the unusual difficulties of a series of operations which, under other circumstances, would have offered nothing peculiarly remarkable. As has already been pointed out, the excavation of the gallery at both ends had already been in operation, by ordinary means, since the latter part of the year 1857; this work continued without interruption until the machinery was ready; and the progress made in that time affords a valuable standard by which to measure the effect of the new machinery. In the interval between the end of 1857 and that to which we have now arrived, namely, the end of 1858, many important works had been pushed forward. At Bardonnêche, the communications had been opened, and bridges and roads constructed for facilitating the transport of the heavy machinery. Houses for the accommodation of the workmen had been rapidly springing up, together with the vast edifices for the various magazines and offices. The canal, more than a mile and a half in length, for conveying water to the air-compressing machines, was constructed, and the little Alpine village had become the centre of life and activity. At Fourneaux, works of a similar character had been put in motion; only here the transport of the water for the compressors was more costly and difficult, the water being at a low level. At first, a current derived from the Arc was used to raise water to the required height, but afterward it was found necessary to establish powerful forcing-pumps, new in their details, which are worked by huge water-wheels driven by the Arc itself. Early in the month of June, 1859, the first erection of the compressing machinery