E63. I ? 
the meafure be not on a level, the 
column of air within the meafure 
may be more or. lefs compreffed. 
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 {mooth furface of  glafs. 
Thefe drops adherin g here and 
there to the infide of this tube 
render its capacity greater or fmaller. 
‘This error may amount to at leaft 
three fub-divifions. 
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 fhut- 
ting the flat flider: for after the 
air is let up into this tube the 
Water runs down its fide for fome 
M 2 time 5 
