[ 2 79 ] 

 degree compbfed of the methods 

 ufed by the two mofi eminent phi- 

 lofophers in this branch of natural 

 knowledge, the Rev. Br. -.Prieftley, 

 and Abbe Fo'ntana. It is this : I 

 let up in the little meafure as much 

 common air as will fill it ; after ' 

 which, I take hold of its brafs 

 flider, and keep it under water ex- 

 actly 15 feconds, when I lift it up 

 till the brafs Aider be on a level 

 with the water of the trough, and 

 ihutthe Aider, to cut oft the column 

 of air within the meafure ; 1 then 

 invert the meafure under water, to 

 let out ail the air' which was re- 

 maining under the Aider. I let uo 

 immediately this meafure of air in 

 the large tube, and fill the little 

 meafure in the fame manner with, 

 nitrous air newly made from red 

 copper, in the manner explained p, 

 T 4 ' . 171; 



