manual labor in the same time. In the year 1862, however, in the three hundred and twenty-five days of actual work, the advance made was raised to three hundred and eighty metres (one thousand two hundred and thirty-five feet), giving a mean advance of 1.17 metres, or about three feet nine inches per day. In the year 1863, the length done (always referring to the South or Bardonnêche side) was raised to above four hundred metres; and no doubt this year a still greater progress will have been made. At the Fourneaux or Northern end of the tunnel--owing to increased difficulties peculiar to the locality--the perforation of the gallery was much delayed. A totally different system of mechanism for the compression of air was necessitated; and it was not before the 25th of January, 1863, that the boring-machine was in _successful_ operation on this side, or two years later than at Bardonnêche. The experience, however, gained at this latter place, and the transfer of a few skilful workmen, soon raised the advance {65} made per day to an amount equivalent to that effected at the Southern entrance. Thus, on the South side (omitting the first year, 1861) since the beginning of 1862, and on the North side since the beginning of 1863, the new system of mechanical tunnelling may be said to have been in regular and _successful_ operation. In the beginning of September of this year were completed in all three thousand five hundred and seventy metres of gallery. From this we deduct sixteen hundred metres done by manual labor, leaving, for the work done by the machines, a length of nineteen hundred and seventy metres. From this we can make a further deduction of the one hundred and seventy metres executed in the first year of experiment and trial at Bardonnêche, so that we have eighteen hundred metres in length excavated by the machines in a time dating from the beginning of 1862 at the South end, and from the beginning of 1863 at the North end of the tunnel. Thus, up to the month of September, 1864, we have in all four years and six months; and eighteen hundred metres divided by 4.5 gives us four hundred metres as the rate of progress per year at each side, or in total, eight hundred metres per year. Basing our calculation, then, on this rate, we find that the eight thousand six hundred and fifty metres yet to be excavated will require about ten and a half more years; so that we may look forward to the opening of the Mont Cenis tunnel at about the year 1875. The directing engineers, who have given good proof of competency and skill, are, however, of opinion that this period may be considerably reduced, unless some totally unlooked-for obstacles are met with in the interior of the mountain. As has been indicated above, sixteen hundred metres in length of the tunnel was completed by manual labor before the introduction of the mechanical boring-engines, in a period of five years at the North and three years at the South side, equal to four