CHAP. IX.] 



THE LOCOMOTIVE. 



475 



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 alter- 

 nately 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 

 contain 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, 8 metres long and 1J metres diameter/supported 

 towards its extremities by two trucks, which, on starting, were filled 

 with condensed air, and which communicated by a tube with the 



Fto. 321. Mechanism for regulating the pressure. 



distributing apparatus of the cylinders. The locomotive 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. At de- 

 parture the pressure in the reservoir was about 7 kilogrammes per 

 square centimetre; the locomotive having drawn a train of twelve 

 loaded waggons along a course of about 600 metres, the pressure was 

 found to fall to 4J kilogrammes ; the train then returned empty to 

 the point of departure, and the final pressure was found to be 2J 

 kilogrammes. 



In spite of the relatively advantageous results which were obtained, 



