40 ANNUAL OF SCIENTIFIC DISCOVERT. 



bankment, it will have the appearance of a ridge extending from 

 shore to shore, about 150 feet wide at the base, 40 feet high, and 

 from 40 to 120 feet below the level of lo*w tide. The tubes would 

 be circular in form, made of iron plates double riveted and caulked 

 as in high-pressure steam boilers, and of the same thickness as the 

 skin-plates of the " Warrior." The tubes would be strengthened 

 by outer iron girder frames, to the outer flanges of which the 

 timber casing would be attached by bolts, the spaces between the 

 casing and the tube proper being filled in with concrete. Three 

 ventilators would be built up, one mid-channel, and one about a 

 mile from either shore ; the mid-channel one a circular mass of iron 

 and stone, 100 feet in diameter, and 210 feet in height, 1G8 feet 

 of which will be below the water-line ; the others would be ordi- 

 nary air-shafts, near the ends of the shore embankments, which 

 would be run out, like breakwaters, about a mile from either 

 shore, to a depth sufficient for navigation over the tubes. 



Of the three classes of propositions for direct communication 

 between England and France, namely, tunnels beneath the bed 

 of the channel, subways through the channel along the bottom, 

 and bridges over the channel, the second appears most reasona- 

 ble, and, with a properly arranged system of submerged tube, 

 possesses many advantages over the others. Mechanics' 1 Magazine. 



THE MONT CENTS TUNNEL. 



From a recent report of the French and Italian Commissioners, 

 it appears that of the total length of the 12,220 metres, equal to 

 7k English miles and 235 yards, there were excavated on 

 the 31st of December, 1866, 3,900 metres on the Italian or 

 Bardeneche side of the mountain, and 2,435 metres on the 

 Modane or French side ; total, 6,335 metres. Between the 1st of 

 January and the 30th of June of the present year, 774 metres 

 were excavated, being the largest number by nearly 200 metres 

 excavated in any one half year since the commencement of the 

 works in 1857. Of the 774 metres, 456 are on the Italian, and 

 318 on the French side; making the total excavated at that date 

 7,109 metres. Ever since the commencement, the progress made 

 on the French side has been slower than on the Italian, on 

 account of a quartz vein ; thus, while, on the 30th of June last, 

 the latter had only to execute 1,754 metres, or about an English 

 mile and a tenth, to accomplish its half, on the French side there re- 

 mained to be excavated 3,357 metres, or nearly 2 miles. If 

 3 metres a day could be excavated on the French side, the per- 

 foration of the tunnel would be accomplished in 3 years and 3 

 weeks ; but as in all probability it will not be proceeded with more 

 rapidly than 2 metres a day, it will require 4 years and 31 weeks to 

 complete it. The tunnel will be lined in its entire length with stone 

 quarried in the immediate vicinity of the two entrances. At the 

 present time the excavations, or headings, are about 1,500 metres in 

 advance of the amount lined. Each metre excavated and lined 

 hitherto has cost, on an average, 11,000 francs, and various cir- 

 cumstances will tend to increase this expenditure as the works pro- 



