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Explanation of the Figures. 



Fig. I. THE great meafure, or 

 great glafs tube, in its fituation in 

 the experiment of examining air, 

 with the brafs fcale upon it, and 

 the magnifier fluck to the brafs 

 tube, on purpofe to adapt accurately 

 the firit mark of the fcale to the 

 '"beginning of the column of air. 

 The glafs tube is fufpended upon 

 the two brafs rings or gingle (in 

 the way the common fea-compafles 

 are fufpended) to keep it always in 

 a perpendicular fituation. AAA A 

 is the brafs tube full of water, in 

 which the glafs tube fixed to the 

 brafs meafure is fufpended. This 

 brafs tube is reprefented tranfparent 

 on purpofe to fee in what manner 

 U 3 the 



