18=t ON THE EXPANSION OF MOIST AIR. 



Exp. i. perforated cork, which was made watertight; and thp edge 



of this end projected about £ a line above that extremity of 

 the cork which entered the bottle, so that the sealed end of 

 the tube, which was out of the bottle, fell 5§ inches below 

 the neck when the bottom was turned upwards. Things be- 

 ing thus prepared, the bottom of the phial wa^ cut away to 

 open a free communication betwixt the atmosphere and the 

 orifice of the manometer. A strong wire was then tied 

 round the bottle, by which it was kept in an oblique posi- 

 tion in a large pan of water, so that the open end of the 

 manometer was 3 inches below the surface. At the same 

 ftime. the interposition of the cork and bottle preserved this 

 aperture dry and exposed to the air. The intention of the 

 preceding arrangement scarcely requires an explanation,for 

 it is evident, that, if the pan were made to boil, the tube 

 would receive all the heat which the water could communi- 

 cate to it, and the size of the boiling vessel was such, as to 

 permit the manometer to be suspended in it free of the sides 

 and bottom, which is a necessary precaution. Lastly, the 

 oblique position of the tube gave the pellet an opportunity 

 to roll over the edge of the orifice, after which it would re- 

 main on the cork, provided the spring of the air proved suf- 

 ficient to expel it. In order to find if this would, really be 

 the case, the pan was gradually heated from 46° to boiling, 

 with the manometer suspended in it: and after the water 

 had continued to boil a few minutes, the instrument was ta- 

 ken out of the pan; upon which the mercury was seen tp 

 descend quickly towards the sealed end of the tube. Ac- 

 cording to this experiment the gas or gasses of the mano- 

 meter were limited in expansion under the pressure of 

 30-185 inches of mercury to twenty times their original 

 bulk at most. Now the advocates of the new hypothesis 

 say, that the vapour alone sustained 30*06 of this force, or 

 the barometrical pressure. Consequently the dilated air 

 supported nothing more than the weight of the, mercurial 

 stopple, or {■ of an inch of mercury. But air ratified 20 

 times will sustain more than if inch of mercury, when the 

 barometer stands at 30-06; neglecting the increased elasti- 

 ritv, which was occasioned in the present instance by raising 



The barony- the pan and its contents from 4t)° to 212°. May not we 



safely 



