Before proceeding to give some account of the Alps Tunnel, it should be stated that it is a national work, and not a commercial speculation. It was originally undertaken by Sardinia, within whose territorial limits it was then wholly included. The cession of Savoy to France brought nearly half the tunnel into French territory, and by the convention establishing the new boundary between France and Italy it was stipulated that this great national work should be continued, should remain exclusively under the control of the Italian engineers, and that France should pay into the Sardinian treasury its proportion of the cost, according to an estimate then made and considered final, and fixed at 3000 francs for each running metre, equivalent to $550 for each running yard of its length in French territory. The work has remained, therefore, as it was, under the exclusive direction of M. Grattoni and M. Sommeiller, the engineers; and a French commission visit the work from time to time, by order of the French government, to view its condition, ascertain its progress, and vouch for the amount to be paid to Sardinia. It is hardly necessary to give a detailed description of the mode by which the compressed air is made to act on the perforating machines at Mount Cenis. The problem was how to get a constant equable supply of air compressed to one-sixth of its ordinary bulk. To effect this a reservoir was constructed at Bardonneche, elevated to a height of eighty-two feet above the works, which furnishes a moving force of two hundred and eight horse power, that being all which is required to operate the drills and ventilate the tunnel. The reservoir is supplied by a never failing mountain stream. From the compressing works, the air is conveyed in a pipe into the tunnel to the drilling machines; another pipe conveying water to wash out the drill holes. At the Fourneaux end of the tunnel, the reservoir is supplied with water by means of pumps.