April 22, 1880] 



NATURE 



583 



about 15 centimetres. It might therefore be assumed 

 that that axis traced in air is of great accuracy. 



As to the operations for verifying the direction within 

 the tunnel, they arc in theory very simple. So long as the 

 boring was not far advanced it was given directly by the 

 direction-points by means of field-glasses fixed in the 

 observatories. At Goeschenen this was done till they had 

 bored to a depth of 1,300 metres, but at Airolo the atmo- 

 sphere was saturated with vapours, and thus they could 



-System of excavation, »J n . i. Advance Gallery ; 2, Side working-; : 

 3. 4, " Cunette de Strosse " ; 5, " Strosse." 



not advance more than 600 m. Beyond those limits, 

 therefore, it was necessary to have several stations. By 

 means of the observatory, lamps were fixed in the exact 

 direction of the axis. Then, a theodolite being placed 

 behind the lamps in a line with them, its telescope was 

 reversed, and the direction thus determined from the 

 bottom of the boring. Lamps were then placed in this line 

 of direction on hooks fastened to the roof of the tunnel. 



They could thus advance and increase the numbers of 

 observing stations as they found necessary, either from 

 the increased length of the boring or the want of trans- 

 parency in the air. This operation, apparently very 

 simple, is in reality very long and complicated, and to 

 effect it various instruments were made use of which were 

 improved during the works. As to the lamps, after trying 

 different modes of lighting, they came back to ordinary 

 petroleum lamps with round wicks, which were placed on 

 stands carefully hung up and centred, and on which the 

 instrument was then placed. To effect communication 

 between the different stations of the instrument and 

 lamps, experience soon proved that the simplest and most 

 economical plan was to use a field telegraph, which was 

 lengthened as they advanced. 



Direction-points were given to the contractor every 200 

 metres, and they were fixed by producing the direction of 

 the preceding points of reference. Twice or thrice a year, 

 however, the operation of tracing the direction from the 

 observatories was recommenced, as if that work had 

 never previously been done ; only when passing under 

 each hook which had been fixed in the previous operations 

 they compared the new result with the preceding, and 

 thus ascertained the changes of direction. In the northern 

 boring the greatest deviation was two centimetres, and 

 that of the south, owing to the vapours, seven. 



The result of that operation was a tunnel 14,920 metres 

 long, starting on the north at the level 1,109, rising at the 

 rate of 5 - S2 in a thousand to the level 1,152, which was 

 attained about the middle of the tunnel, and a small level 

 being left in case of any possible error in levelling, it fell 

 at the rate of 2 in a thousand to the level 1,145 at tnc 

 Airolo station. 



Having thus indicated how the direction of the tunnel 



Ftc. 4.— The borers at work. 



was traced, let us examine the procedure employed in the 

 works properly so called. 



After the experiment made in Mont Cenis, they had 

 only to follow it and at the same time take advantage of 

 the improvements since made on the system ; the two 

 principles without which the work would have been im- 

 possible being mechanical perforation of mine-holes and 

 the transmission of force by compressed air. 



Without the English invention of machines for boring 

 rocks, the opening of a long tunnel without shafts or 



external openings would have occupied so long a time 

 that no company could undertake it. But, thanks to the 

 experiments made elsewhere, M. Louis Favre, the con- 

 tractor of the tunnel, was able to utilise those excellent 

 boring machines which have powerfully assisted in 

 hastening the work. His object was constantly in the 

 direction of suppressing hand-boring, and he almost 

 attained it by making use of several models of machines 

 which cannot be described here, but which are distin- 

 guished by the names of their inventors,* Dubois and 



