NATURE 



{April 22, 1880 



Francois, Ferroux, Mackean, and Turrettini. All these 

 machines have one common object, to project forcibly, 

 and with blows of the greatest rapidity, a tool against the 

 rock, and, as it is drawn back, force it to rotate slightly 

 on its axis. Some of the machines advance by an auto- 

 matic movement; others require a workman to push 

 them. But to keep these boring machines in action some 

 considerable motive power is necessary, and in the Alps 

 that motive power can only be water. The question, 

 then, is How to collect it and transmit it into the 

 tunnel ? 



Close by the Goeschenen opening runs the River Reuss, 

 which has just passed under the legendary "Devil's 

 Bridge," and precipitates itself into its narrow and rocky 

 bed with an average fall of 10 per 100, forming a volume 

 of water which is never less than 1,000 litres per second. 

 M. L. Favre utilised a large rock standing in the channel 

 to fix his dam, below which the water is received in a 

 reservoir to deposit its sand and gravel. Thence it is led 

 to the machines by a cast-iron pipe 'S5 m. in diameter 

 and 800 m. long. The useful fall from the pipe is 85 m. 

 and it can supply 1,200 litres a second. This water works 

 four Girard wheels with horizontal axes. Their diameter 

 is 2"4; they revolve 160 times a minute, and are each of 

 250 to 280 horse-power. When turning a horizontal axis 

 with cranks and wheels attached, the number of revolu- 

 tions is reduced to So per minute. 



At Airolo, the nearest river being the Ticino, which has no 

 rapid descent, it would have required a very long canal to 

 procure enough of fall. M. Favre therefore followed the 

 advice of engineers who had studied the matter and 

 assured him he would find enough water by making use 

 of the Tremola, a torrent close by the tunnel, which falls 

 into the valley with an average descent of 20 per 100 

 and is said to supply at least from 300 to 400 litres a 

 second at the bottom. By collecting the water at a 

 height sufficient to allow of the receiving reservoir giving 

 a useful ^fall of 180 m., the necessary motive power could 

 thus be found. The works were completed in 1872, but in 

 February, 1873, the supply of the Tremola fell to 100 

 litres, and there was not sufficient power to turn the water- 

 wheels. This did not last long, it is true, but the same 

 scarcity of water reappearing next year, M. Favre resolved 

 to form an auxiliary supply by collecting the Ticino water 

 3 kilometres up the river, and thus have a new fall in 

 order to meet all eventualities. By this means four 

 tangential water-wheels with vertical axes are turned ; 

 they are of bronze, with a diameter of vi m., and revolve 

 350 times a minute, each being of about 200 horse-power. 

 By means of conical gearing they turn a horizontal axis 

 with cranks revolving 85 times a minute. When the 

 supply of the Ticino is insufficient, it is made to act on a 

 smaller number of wheels ; and then on the vertical axles, 

 which are no longer turned by that stream, there are other 

 water-wheels slightly different on which the water of the 

 Ticino is brought to bear. 



The power communicated to the horizontal axis at each 

 opening is transmitted into the tunnel by means of the 

 remarkable system already employed at Mont Ccnis, and 

 the inventor of which is Prof. Colladon of Geneva. This 

 engineer conceived the idea of using for that purpose 

 compressed air. The immense advantage gained by it is 

 the transmission of a motive power, whatever the tem- 



perature or distance may be ; moreover, it serves for 

 ventilation and the supply of fresh air. 



But the compression of air develops great heat, which 

 injures the machine. At Mont Cenis, to avoid this 

 heating, the air was compressed by means of pistons of 

 cold water, which were themselves pushed by ordinary 

 pistons moving up and down in pump cylinders. In 

 order that the piston pushing the water should move it 

 without splashing it must itself be moved very slowly, 

 and the quantity of air required being considerable, the 

 slowness of the movement must be compensated by the 

 size of the pumps. At St. Gothard the following new 

 invention of M. Colladon was utilised to prevent the tem- 

 perature from becoming too high. The body of the com- 

 pression-pump is double, and between its outer and inner 

 cylinder circulates a current of cold water introduced by- 

 pumps. This cold water also circulates in the hollow rod 

 of the piston and in the piston itself, which is also hollow. 

 Moreover, cold water under the form of fine dust is injected 

 even into the interior of the body of the pump, and then 

 expelled by each stroke of the piston along with the com- 

 pressed air. In this manner air compressed at 8 atmo- 

 spheres only assumes a temperature of 32 C, which is 

 lowered in the reservoirs to which it is exposed before 

 passing into the tunnel. By this ingenious arrangement 

 we can give much more rapidity to the pistons and 

 proportionately diminish the volume of the pumps. 



At Airolo and Goeschenen there are fifteen such pumps, 

 divided at each place into five groups of three. They are 

 horizontal, and their pistons are set in motion by beams 

 connected with the cranks of the main axis. They serve 

 a double purpose : at the bottom of each pump cylinder 

 there are two expiration valves and one for supply. The 

 Airolo pumps are of '46 m. interior diameter, and at each 

 stroke of the piston (through '45 m.) a pump receives 71 

 litres of air, and by compression reduces this volume to 

 a seventh part. In this manner, when the supply is ade- 

 quate (160 litres for each wheel), four groups of three 

 pumps (one of the five groups being generally left at rest) 

 receive in twenty-four hours 208,000 cubic metres of air, 

 whereas the volume required is 104,000. At Goeschenen 

 the pumps are of '42 m. diameter, and at each stroke of 

 the piston (through "65 m.) 87 litres are received ; but the 

 number of strokes of the piston is rather less. 



The compressed air is sent into reservoirs, where it is 

 cooled, and the water in suspension deposited. Thence 

 it is conducted by tubes into the tunnel. These con- 

 ducting tubes are pipes of hammered iron of - 20 m. 

 diameter, which are bolted together end to end, and 

 placed all along the tunnel. At each new stage of 

 the work the expenditure of air diminishes as they 

 advance, and the diameter of the pipes is accordingly 

 reduced to - I4, then to 'lo, till at last they terminate in 

 india-rubber tubes of 5 centim., which supply the com- 

 pressed air for working the advanced gallery. 



The process being now known, let us examine how 

 the work is organised. The tunnel being 8 m. wide 

 and 6 m. high above the rails, since it must be vaulted, 

 it is necessary to make a clearance as high as 61- m. 

 above the rails. The first thing is to make a prelimi- 

 nary or advanced boring 2k m. high and 2i m. broad. 

 For this first boring M. Favre adopted the Belgian system, 

 according to which the preliminary gallery isentirely at 



