300 PRESSURE IN THE AIR, 



adjusted as was possible, having an aperture 

 for the passage of the tube, and found that it 

 required the additional weight of 10 ounces and 

 6 drachms to raise the mercury in the tube one 

 quarter of an inch, that is to say, from 29^ 

 inches, to 29f . With a view of varying these 

 experiments, and to obtain additional evi- 

 dence, that it is the pressure of expansibility 

 and not the pressure of weight which air exerts 

 when the equilibrium is destroyed, as is the case 

 in exhausted media in general, and in the Torri- 

 cellian vacuum, as it is improperly called, in 

 particular; I took equal and separate portions 

 of different gases, whose relative weights are 

 Jknown to be different from each other, I in- 

 closed each gas separately in each bladder, and 

 screwed the bladder as before to the receiver in 

 which the Torricellian tube was placed ; one 

 bladder contained hydrogen gas, 2nd, oxygen 

 gas, 3rd, atmospherical air, and 4th, carbonic 

 acid gas ; the tubes were of the same lengths, 

 but the' bores were different ; varying in size, 

 from % of an inch, to 1 inch in diameter. 

 On exhausting the air which the receiver con- 

 tained, the mercury in all sunk in the same 

 time from 29^- inches to the same level as the 

 mercury in the basin : on admitting each gas 

 to each tube, it was uniformly found, that nei- 

 ther the difference in the weight of the gas, nor 

 the difference of the bore in the tube, produced 



