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THE POPULAR SCIENCE MONTHLY 



of the galleries prevents effectual ventilation. The high price of 

 horses and the large number required prevent their use. The idea 

 suggested itself of making use for St. Gothard of machines moved by- 

 compressed air, which would have many advantages. First, it is well 

 known that compressed air is used to work the perforating machines 

 used in boring the tunnel ; then, by the employment of compressed-air 

 locomotives, ventilation of the galleries would be produced, as these 

 machines would allow only pure air to escape ; and then these motors 

 would be more powerful than horses, and effect more rapidly the clear- 

 ing away of the debris. 



Fig. i. 



A first attempt was made in which two ordinary locomotives were 

 employed, one at each side of the tunnel; the boilers, in which, of 

 course, there was no water, were filled with condensed air under a 

 pressure of four atmospheres. This air played the part usually done 

 by steam, passed into slide-valves, entered the cylinders alternately 

 on each face of the pistons, which it set in motion, and then escaped 

 into the atmosphere. 



It is easily seen that, if compressed air were to be employed, it 

 would be indispensable to have a very considerable quantity of it; the 

 boiler of a locomotive, sufficient when it is worked by means of steam 

 constantly produced under the action of heat, was too small to con- 

 tain a quantity of air sufficient for use without being filled. This led 

 to adding to each locomotive a special reservoir for compressed air; 

 each locomotive was accompanied, as a kind of tender, by a long 

 sheet-iron cylinder, eight metres long and one and a half metre di- 

 ameter, supported toward its extremities by two trucks, which, on 

 starting, were filled with condensed air, and which communicated by 

 a tube with the distributing apparatus of the cylinders. The loco- 

 motive then worked as before, except that compressed air came from 

 the reservoirs instead of from the boiler. The two locomotives, the 

 Reuss and the Tessin, worked economically for about two years, in 

 spite of the awkwardness of the long cylinders that accompanied 

 them. We can give some interesting figm'es resulting from the mean 

 of a certain number of observations. At departure the pressure in 



