[ 'i6* ] 



I. The firfr. error may be com- 

 mitted by the hand, which, by 

 touching this tube in the time of 

 filling it with air, may expand this 

 air by communicating its heat to it. 

 The refult of this error may amount 

 to two fub-divifions. 



II. The fecond error may be com- 

 mitted alfo by the warmth of the 

 hand in which this meafure is kept, 

 when it is raifed till the flat Aider 

 is on a level with the furface of 

 the water, in the moment it is 

 pufhed in to cut the column of air 

 within the meafure from the air to 

 be fhut out. This error may alfo 

 amount to two fub-divilions. 



III. The third error may be com- 

 mitted by not keeping the meafure, 

 in the moment of fhutting the flider, 

 exactly at the height required ; for, 

 if the water within and without 



the 



