[ 163 ] 



the meafure be not on a level, the 

 column of air within the meafure 

 may be more or lefs comprefTed. 

 This error may amount to four fub- 

 divifions. 



IV. The fourth error may depend 

 upon the infide of this tube not be- 

 ing made rough by emery ; for 

 water fettles in the form of drops 

 on the fmooth furface of glafs. 

 Thefe drops adhering here and 

 there to the infide of this tube 

 render its capacity greater or fmaller. 

 This error may amount to at leaft 

 three fub-di virions. 



V. The fifth error depending on 

 this meafure may be owing to the 

 difference of time between the fill- 

 ing this tube with air and the Ihut- 

 ting the flat Aider : for after the 

 air is let up into this tube the 

 water runs down its fide for fome 



M 2 time ; 



