MECHAXH S AND USEFUL ARTS. Gl 



to recoi'd some interesting facts which might, perhaps, never have been dis- 

 covered but for the peculiar methods employed in this colossal operation. 

 Modane and Bardoneche are situated on opposite sides of the Alpine chain 

 which divides Piedmont from France, and precisely at a point where the val- 

 leys of the Arc and the Dora, which lie nearly on the same level, run paral- 

 lel to each other, and the mountain is narrowest. The thickness of the 

 intervening mountain is 13 kilometres in a straight line ; the actual tunnel 

 will be 12 1-2 kilometres. It is designed in the same vertical plane, but, to 

 facilitate drainage, is somewhat higher in the middle than at the orifices, so as 

 to form gentle slopes on both sides, one not exceeding an inclination of five 

 per thousand, and the other being twenty-three per thousand, in consequence 

 of a difference of level between the two extremities, the numbers being, 

 Bardoneche (southern orifice), 1,324 meters; culminating point, 1,335 meters; 

 Modane (northern orifice), 1,190 meters above the level of the sea. The crest 

 of the mountain being 1,600 meters higher than the culminating point, the 

 sinking of shafts which is the method generally employed in order to 

 begin boring tunnels at several points at once was out of the question; 

 hence the tunnel could only be worked at its extremities, so that the labor, 

 by the ordinary processes, could not be accomplished in less than thirty -six 

 years. Then, how was a depth of gallery of three or four kilometres, and 

 having but one orifice, to be aired? These were all serious obstacles. MM. 

 Elie de Beaumont and Angelo Sismonda having examined the mountain 

 geologically, found it to contain micaceous sandstone, micaceous schists, 

 quartzite, gypsum, and limestone, all easy to blast, the quart/ite alone ex- 

 cepted; but the stratum of this is not likely to be very thick. The other dif- 

 ficulties alone, therefore, remained; and these were at length overcome b) r 

 three Sardinian engineers, MM. Sommeiller, Grattone, andGrandis, who 

 proposed to turn the abundance of Avater for which the locality was remark- 

 able to account, by applying it to a peculiar system of perforation and venti- 

 lation, which we will now endeavor to explain. The first apparatus imagined 

 by these gentlemen consists in a hydraulic air-condenser, which is a syphon 

 turned with its orifices upward, and' communicating by one of them with a 

 stream of water, by the other with a reservoir of air. The water, descend- 

 ing into the first branch, enters the second, and by the pressure it exercises 

 condenses the air, which is then forced into the reservoir. This done, a valve 

 is opened, by which the water contained in the syphon is let out, and the 

 operation recommences. The emission and introduction valves are regulated 

 by a small machine operating by means of a column of water; and the air 

 in the reservoir is maintained at a constant degree of pressure by a column 

 of water communicating with another reservoir above. Thus, with a water- 

 fall twenty meters in height, the air is condensed to six atmospheres, equiv- 

 alent to the pi'essure of sixty-two meters of water. This condensed air is 

 used for two purposes; first, as a motive power, and then for ventilation. 

 Two kinds of perforators, worked by condensed air instead of steam, are em- 

 ployed, one invented by Mr. Bartlett, the other by M. Sommeiller, and the 

 manner in which these machines perform their duty affords the first practical 

 demonstration of the possibility of employing compressed air as a motive 

 power with advantage. By means of these perforators holes for blasting 

 may be bored through the hardest sienite in one-twelfth of the time which 

 would be required if ordinary means were employed. In order to understand 

 the importance of this result, it may be stated that, in tunneling, three-fourths 



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