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cautions to be obferved, which I 

 extracted from the manufcript of 

 the author. 



He reduces the various fources 

 from which errors may arife in this 

 manner of exploring air to twenty ; 

 which are, however, not all of equal 

 importance, and may counterbalance 

 in fome meafure one another, fo 

 that one error may correct another. 

 But fome of thefe are of fuch im- 

 portance, that by overlooking them 

 it may happen that the befl. atmo- 

 fpheric air fhall appear to be a true 

 poifonous one. 



Thofe errors may originate prin- 

 cipally either from the great tube 

 or meafure, or from the little mea- 

 fure. 



The errors which may originate 



from the fmall meafure are feven : 



M I. The 



