32 AVNUAI. OF SCIENTIFIC DISCOVERT. 



of the rivor to sailiiifj oraft of all descriptions, thus avoid in";' (lie 

 almost intcrniinalilc d(days now caused b}' the constant swin<j:ing 

 of the various l)nd2;es during the season of navigation, as well as 

 the many accidents which are sure to result from our present 

 bridge system. 



The longest tunnel in England is the Box Tunnel on the Great 

 Western Railwa}-, wliich is 9,080 feet long, 39 feet high, and 35 



feet wide. 



SAXD-rATCH TUIOfEL. 



The miners working in the middle section of the Sand-Patch 

 Tunnel, on the Pittsburg and Connellsville Railroad, have met, 

 tluis piercing once more the great mountain l)arrier l)etween the 

 Ohio valley and the sea-board. Tiie Saiid-rateh Tunnel is 4,750 

 feet long, or 1,000 feet longer than the Alleghanj'-Mountain Tunnel 

 of the Pennsylvania Railroad. It was commenced some ten 

 years ago, is to accommodate a double track of rails all through, 

 being '22 fc(>t Avidc, and 19 feet high. The greater portion of it 

 goes through solid red sand-stone, not requiring any l)rick arch- 

 ing for that distance. The grade of the tunnel is 2,200 feet above 

 the level of the sea, or 1,500 feet higher than low-water mai"k of 

 the Ohio I'iver at Pittsburg. 



TUB MOXT-CENIS TUNNEL. 



It is estimated that the number of holes which have to be 

 drilled by the rock-boring machines in the IVIont-Cenis Tunnel, 

 before that work is completed, is about 1,600,000. The total 

 depth of all these holes when bored will amount to about 4,265,- 

 890 feet, which is 105 times the length of the tunnel. Nearly 13,- 

 000,000,000 IjIows will be struck by the perforators, to d() tiiis 

 "work. The entrance to the tunnel, on the French side, is 3,946 

 feet above the level of the sea, and its termination, on the Italian 

 side, 4,380 feet, so tliat the actual difference of level between the 

 two extremities is about 434 feet. 



The total length of the Mont-Cenis Tunnel is 12,220 metres ; of 

 this, 7,977 remain to be made. Having been begun in 1858, and 

 with new methods and energy in 1863, 4,423.4 metres were fin- 

 ished on the first of April, 1«65 ; of which, 1,640 metres were ac- 

 complished by the old methods of tunnelling, and 2,777.4 bj^ the 

 new mechanical methods, since the commencement, of 1863 — 802 

 metres in 1863; 1,088 in 1864; and 337.4 in the first quarter of 

 1865. The rate of progi-ess in 1862 was 2.02 metres per day ; in 

 1864, 2.92 metres, and in 1865, thus far, 3.75. At the last rate, it 

 will take 5 2-3 years to complete the tunnel. 



Air is compressed by w^ater-power outside, and is conveyed by 

 pipes into the excavation, where it gives motion to the chisels 

 that pei-forate the rock, forming cavities for the gunjiowder used 

 in blasting. Small pei'forators travel on a carriage, each of them 

 being a kind of horizontal air-pressure engine, the jjrolonged 

 piston-rod of which carries a jumper, that makes 250 strokes a 

 minute. The excess of pressure on each jumper, above that of 

 the air-spring which brings it back, is 216 lbs., thus bringing a 

 very considerable power into action. 



