ENGINEERING. 



281 



ner roads cross the chain at comparatively low 

 altitudes and their tunnels are much shorter. 

 The fifteen tunnels of the Semmering aggregate 

 together 4,469 metres, and of the twenty-seven 

 tunnels of the Brenner, the largest is only 885 

 metres. The Mont Cenis Tunnel is 12,233 me- 

 tres. The St. Gothard Tunnel is 14,944 metres 

 in length, and besides the main tunnel there 

 are fifty-three others, making altogether 40,- 

 718 metres of tunneling. 



The French, as stated in another place, are 

 considering the project of a new railroad con- 

 nection with Italy, either through the Simplon, 

 Mont Blanc, or Little St. Bernard, in order to 

 retain the through French traffic which the St. 

 Gothard Railroad threatens to take away. The 

 Government engineers reported in favor of the 

 Mont Blanc route, the ground of their prefer- 

 ence being that the mouth of the tunnel would 

 be in French territory, while by the Simplon 

 route it would be necessary to use Swiss rail- 

 ways for 127 miles, and that it would preserve 

 to Marseilles its Swiss trade, which would oth- 

 erwise go to Genoa. The Simplon route does 

 not present the same engineering difficulties as 

 Mont Blanc, but still it would require sixty miles 

 of mountain railway and a tunnel twelve and a 

 half miles long, exceeding by more than three 

 miles the great St. Gothard Tunnel. The high- 

 est elevation would be 2,205 feet, which is much 

 lower than that of the St. Gothard (3,693 feet), 

 the Mont Cenis (4,043), or the Arlberg Tunnel 

 (4,102); but the difficulty of cooling the tun- 

 nel would be so much the greater. The tem- 

 perature in the St. Gothard Tunnel is 31 Cen- 

 tigrade, and under the Simplon would be three 

 or four degrees hotter. Calculations as to the 

 temperature of the projected tunnel under 

 Mont Blanc indicate a temperature of 55 Cen- 

 tigrade for the distance of two miles, but 

 there are -better facilities for ventilation than 

 in the St. Gothard Tunnel, since, for the dis- 

 tance of about three miles, ventilation-shafts 

 640 feet deep will connect it with the outer 

 air. The Mont Blanc railway would involve 

 the outlay of about 179,000,000 francs, and the 

 one over the Simplon would cost 145,000,000 

 francs. 



The Arlberg Tunnel, to connect Switzerland 

 with the Austrian railway system, which was 

 begun in June, 1880, will be 6'382 miles long. 

 The summit-level, 4,998 feet above the Adriatic, 

 is 2-611 miles from the eastern extremity. The 

 Ferroux machine, which was employed in the 

 St. Gothard Tunnel, is used at the eastern end, 

 and the Brandt machine, which was tried with 

 good results in the St. Gothard works, is em- 

 ployed at the other end. The latter was guar- 

 anteed by the inventor to advance six feet four 

 inches a day. Its performance greatly exceeds 

 the guarantee. It drills by boring, and is moved 

 by water under pressure, while the Ferroux 

 perforator acts by percussion and is propelled 

 by compressed air. The comparison of the 

 I two, working under identical conditions, will 

 enable engineers to determine which is the 



preferable system. The ventilation of the Arl- 

 berg works will be accomplished by a separate 

 apparatus, distributing air under low pressure 

 through pipes at the point where the work is 

 going on. 



With the ingenious machine of Colonel 

 Beaumont a gallery seven feet in diameter has 

 been driven for the distance of over a mile and 

 a quarter from the English shore in the gray 

 chalk underneath the English Channel. The 

 Beaumont perforator consists of a powerful 

 bar of iron rotated about its center, with seven 

 short teeth or knives of steel on each arm 

 which scratch away the chalk from the face 

 of the heading. At each turn of the bar the 

 machine is impelled forward on a horizontal 

 axis through a distance of seven millimetres, 

 or about a quarter of an inch. The heading 

 driven by the perforator is 2'14 metres in di- 

 ameter and perfectly cylindrical. The axle on 

 which the bar that carries the knives rotates 

 is a powerful bar of steel. The rotary move- 

 ment is given to it by means of a system of 

 cog-wheels which successively reduce the speed 

 originally imparted by compressed air to the 

 actuating crank and communicated to the cog- 

 wheels by a pair of friction cylinders. The 

 horizontal movements of the machine are pro- 

 duced by a hydraulic apparatus, and are con- 

 trolled by valves which allow the machine 

 to be moved forward or backward, or to re- 

 main on one spot. When the machine has 

 advanced by hydraulic pressure through a dis- 

 tance of. 6 feet, the machine is lifted off its 

 bed by a combination of levers, and the hy- 

 draulic pressure is applied to the bed of the 

 machine, moving it forward another stage. 

 The rock is very finely divided by the knives of 

 the perforator. The fragments fall to the floor 

 of the gallery, and are gathered up by large 

 scrapers and conveyed to cars at the back of 

 the machine by buckets attached to an endless 

 chain. The crank-axle makes 100 revolutions 

 a minute, with a pneumatic pressure of two 

 atmospheres, or 45 pounds to the square inch. 

 The actual progress of the machine on the 

 English side averaged 60 centimetres an hour 

 and 15 metres a day. A more powerful ma- 

 chine is used on the French side, which accom- 

 plishes one metre an hour. 



The execution of the New York Tunnel in 

 the soft, silty bed of the Hudson River, be- 

 tween Jersey City and New York, is still prob- 

 lematical, as the works have stopped for the 

 second time. The erroneous idea that com- 

 pressed air would act as a support instead of 

 timbering resulted in the distressing accident 

 by which a number of men lost their lives a 

 short time after the tunnel was begun. After 

 that a permanent bulk-head of masonry was 

 constructed near the shaft, containing an air- 

 lock, consisting of an iron tube large enough 

 for the admission of a man. The ingenious 

 plan on which the tunnel is constructed has 

 been before described. The plate-iron shell, 

 within which the arched masonry is built, has 



