noyi'CondudVing Powe^ of a perfedl Vacuum, 2*^5 



of the fluid entirely, without employing violence, v/hich is 

 the cafe in common and condenfed air, but more particularly 

 in the latter. Thele experiments, however, belong to another 

 fubje6t, and may poffibly be communicated at Ibrae future 

 time. 



It is furprifing to obferv^e, how readily an exhaufted tube is 

 charged with eledricity. By placing it at ten or' twelve inches 

 from the conductor the light may be feen pervading its in{ide,and 

 as ftrong a charge may fometimes be procured as if it were in 

 contact with the condudlor: nor does it fignify how narrow the 

 bore of the glafs may be ; for even a thermometer tube, having 

 the minuteil: perforation poffible, will charge with the utmoft 

 facility ; and in this experiment the ph'jenomena are peculiarly 

 beautiful. 



Let one end of a thermometer tube be fealed hennetically. 

 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 exhaufted, let the fealed end be applied 

 to the conductor of an electrical machine, while the other end 

 is either held in the hand or conne£ted to the floor. Upon the 

 flighteft excitation the eleCtric 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 inceffantly 

 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 

 thatlengtli. If, inftead of the fealed end, a bulb be 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 j but in this cafe 

 1 have feldom been able to repeat the trials above three or four 



N n 5 times 



