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X. On an Improvement in the Air-Pump. 



Park. 



By the Rev. J. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 'VT'OU will oblige me by inserting in your Journal the fol- 

 -*■ lowing brief description of an improvement in the con- 

 struction of the air-pump. 



A model in my possession works very satisfactorily ; but, 

 from want of opportunity, I have not been able to compare 

 its efficiency with other instruments already in use. It con- 

 sists of a barrel or cylinder of iron truly bored and polished. 

 To this cylinder is accurately fitted a case-hardened iron piston, 

 in the usual manner, the piston-rod working at the upper end 

 through a collar of oiled leathers, perfectly air-tight. At a 



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I 



distance from each end, exceeding a little the length of the 

 piston, are a number of very small apertures, for the admis- 

 sion and egress of the air. At the lower end is another accu- 

 rately fitted metallic plug, the end of which is perfectly flat, 



