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SCIENCE PROGRESS 



35 ft. It may be expected therefore that as the compression 

 pressure increases the efficiency will also increase ; there is 

 every reason to believe that when the compression pressure 

 reaches that employed in ordinary gas engines, the best 







Compression pressure in lb. per sq. in. above atmosphere. 

 Fig. io. — Practical efficiency curves: 071 of air standard. 



efficiencies attained in gas engines will be reached and probably 

 surpassed by the Humphrey pump. 



Readers who desire to study this subject in greater detail 

 may be referred to Mr. Humphrey's papers, especially to that 

 read before the Manchester Association of Engineers last year. 





