Spuljic Gravities of Alloys of Tin and Lead. 



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De/crlptient of the Improved Air Pumps of PsiNCB. and CuTHBERTSON ; luith Ohfervations. 



X. HE important ufes of the Air Pump are too many and too well known to require enu- 

 meration. It is an engine, not only calculated to demonftrate many of tJie leading princi- 

 ples in natural philofopliy, but indifpenfable for the performance of fome of the mod accu- 



