LOCOMOTIVE, COMPRESSED-AIR. 



479 



being frequently filled. This led to adding to 

 each locomotive a special reservoir for com- 

 pressed air, which, mounted on trucks of its 

 own. became a kind of tender, the air in the 

 reservoir being conveyed by a tube to the dis- 

 tributing apparatus of the cylinders. The loco- 

 motive then worked as before, except that com- 

 il air came from the reservoir instead of 



from the boiler. Two locomotives were thus 

 worked economically for about two yearn, in 

 spite of the awkwardness of the long reser- 

 voirs that accompanied them. At departure 

 the pressure in the reservoir was about seven 

 kilogrammes per square centimetre; the loco- 

 motive having drawn a train of twelve loaded 

 wagons along a course of about 600 metres, 



the pressure was found to fall to four and a 

 half kilogrammes ; the train then returned 

 empty to the point of departure, the final 



gressure being two and a half kilogrammes, 

 ut by this arrangement it was found to be 

 impossible to suitably regulate the pressure of 

 the air between the reservoir and the distribut- 



ing apparatus: to get over this difficulty II. 

 Ribourt, the engineer of the tunnel, devised 

 an arrangement which allows the compressed 

 air to flow at a fixed pressure, whatever the 

 pressure in the reservoir. The air in escaping 

 from the reservoir enters a cylinder B (Fig. 1), 

 over a certain extent of the walls of which 



