ndn^eonduffiitig V.6W.er oj' a perfedi Vacuum, ^ 
of the fluid entirely, without employing violence, which is 
the cafe in common and condenfed air, but more particularly 
in the latter. Thefe experiments, however, belong to another 
fubfed, and may poffib'iy be communicated at fame future 
time. 
It is furprifing to obferve, how readily , an exhaufted tube is 
charged with electricity. By placing it at ten or twelve inches 
from the conductor the light may be feen pervading its infide,and 
as drong a charge may fometimes be procured as if it were in 
contact with the condudlorp nor does it fignify how narrow 7- the 
bore of the glafs may he ; for even a thermometer tube, having 
the minuted: perforation poffible, will charge with the utmod 
facility ; and in this experiment the phenomena are peculiarly 
beautiful. 
Let one end of a thermometer tube be fealed hermetically. 
Let the other end be cemented into a brafs cap with a valve, 
or into a brafs cock, fo that it may be fitted to the plate of an 
air-pump. When it is exhauded, let the fealed end he applied 
to the conductor of an eledtrical machine, while the other end 
is either held in the hand or connefled to the floor. Upon the 
flighted excitation the ele&ric fluid will accumulate at the fealed 
end, and be difcharged through the infide in the form of a 
fpark, and this Accumulation and difcharge may be inceflantly 
repeated till the tube is broken. By this means I have had a 
fpark 42 inches long, and, had I been provided with a proper tube, 
I do not doubt but that I might have had a fpark of four times 
that length. Jf, indead of the fealed end, a bulb l^e blown at that 
extremity of the tube, the eleftric light will fill the whole of 
that bulb, and then pafs through the tube in the form of a 
brilliant, fpark, as in the foregoing experiment 5 but in this cafe 
I have feldom been able to repeat the trials above three or four 
N n 2 times 
