fonts Experiments made with an Air-pump. 643 
meter-gages, that the remaining contents of a receiver, 
when exhaufted as much as poffible, was at different 
times of different kinds ; fometimes it feemed to confift 
entirely of permanent air, as when a little vitriolic acid, 
&c. was put in the receiver; and fometimes moftly of 
vapour arifing from moifture, and but a very fmall pro- 
portion of permanent air, as when a bit of damp leather, 
Sec. was in the receiver. I was now therefore defirous of 
feeing what appearance the eledtric matter would exhibit 
in thefe different rarified media. 
For this purpofe I had a glafs tube made, of an inch 
bore, and four feet and a half in length. This tube was 
connedted to the receiver of the air-pump by means of 
an elbow-piece of brafs,to which it was cemented ; which 
elbow-piece was inferted perpendicularly in the top of 
the receiver : as the elbow made a right angle, the tube 
itfelf was of courfe horizontal. 
Moreover, at that end of the glafs tube which was 
cemented to the brafs elbow-piece, there was fixed, on 
the infide, a piece of brafs wire, about three inches and 
a half long, filed to a point, and pointing towards the 
other end of the tube. At the other end of the tube was 
cemented a brafs fcrew fitted to a brafs cap, which 
fcrewed on it; and in this brafs cap was fixed a brafs 
wire, three inches and a half long, which pointed towards 
40a the 
