C 283 ] 



A glafs tube longer than that? 

 which I had at hand would bear 

 a larger fcale, and thus indicate 

 with Itill more accuracy the good- 

 neis of the air : but the two mea- 

 sures of air let up muft not 



more than one half of the glafs 

 tube, for otherwife it could not be 

 fhook in the water without danger 

 of fome bubbles of -air coming out 

 of it, or ruming in it, by the force 

 of making it up and down. 



In the works of the Rev. Dr. 

 Prieftley, one meafure of common 

 air is faid to occupy fometimes 120, 

 and even more fubdiviiions, which 

 is owing to his peculiar method. 

 He firffc joins the two airs together 

 in a feparate jar, and allows them 

 to ftand a certain time to incorpo- 

 rate one with the other ; after 

 which, he lets them up in his large 



tube 



