ventilating and purifying the gallery. The air is conducted in pipes about eight inches in diameter, having a thickness of metal of about three-eighths of an inch. Much doubt had previously been expressed as to the possibility of conveying compressed air to great distances without a very great and serious loss of power. The experience gained, however, at the Mont Cenis has shown that, conveyed to a distance of thirteen English miles, the loss would be but one-tenth of the original force; and that the actual measured loss of power in a distance of six thousand five hundred feet, a little more than a mile and a quarter, was less than 1-127th of the original pressure in the recipients. The mouth of the tunnel is but a few hundred yards from the air-compressing house--we will now proceed thither. For nearly a mile in length the gallery is completed and lined with masonry. At the first view, we are struck with the bold outline of its section and its ample dimensions. Excepting, perhaps, the passage of an occasional railway-truck, laden with pieces of rock and rubbish, we find nothing to remind us of the numbers of busy workmen and of the powerful machines which are laboring in the tunnel. All is perfectly quiet and solitary. Looking around us as we traverse this first and completed portion, we observe nothing very different from an ordinary railway-tunnel, with the exception of the great iron pipe which conveys the compressed air, and is attached to the side of the wall. At the end of about a quarter of an hour we begin to hear sounds of activity, and little lights flickering in the distance indicate that we are approaching the scene of operations. In a few moments we reach the second division of the tunnel, or that part which is being enlarged from the comparatively small section made by the perforating-machine to its full dimensions, previously to being lined with masonry. In those portions where the workmen are engaged in the somewhat dangerous operation of detaching large blocks of stone from the roof, the tunnel is protected by a ceiling of massive beams, under which the visitor passes--not, however, without hurrying his pace and experiencing a feeling of satisfaction when the distance is completed. Gradually leaving behind us the bee-like crowd of busy miners, with the eternal ring of their boring-bars against the hard rock, we find the excavated gallery {69} getting smaller and smaller, and the difficulties of picking our way increasing at every step; the sounds behind us get fainter and fainter, and in a short time we are again in the midst of a profound solitude.