824 REPORT— 1888. 



4. A new form of Air-compressor for Variable Pressures} 

 By H. Dayey, M.Inst.C.E. 



This is an air-pump capable of automatically maintaining a constant resistance 

 when pumping against an increasing or decreasing pressure. 



One of its applications is that of compressing air for storage purposes. 



It is evident that if an ordinary air-pump be made of sufficient capacity to take 

 the full power of the engine employed to drive it at the minimum pressure, it will 

 be too large for the increasing pressure ; and, on the other hand, if the pump be 

 made small enough for pumping against the maximum pressure, it will only take 

 up a portion of the power of the engine at the lower pressures. 



The problem then is to construct an air-pump which shall work with a constant 

 resistance against increasing and decreasing pressures. It is evident that if the 

 weight of air per stroke of the air-pump could be made to vary inversely with the 

 varying pressures against which the pump works (in proper proportions) then the 

 engine would have a constant resistance, and its full power might be employed 

 during the whole of the operation. This Ls effected by mechanical means, described 

 and illustrated in the paper. The resistance of the pump governs the engine. The 

 engine runs without a throttle valve and with varying steam pressures at a constant 

 speed, always fully utilising the full power available, and thereby doing the work 

 in the shortest time with the greatest economj- of power. 



5. On controlling the direction of Rotation of a Dynamo. By A. Winter. 



See Enginceriuij , vol. xlvi. p. 413. 



