6 Mr. W. G. Armstrong on the Cause of the 



already published an account, I felt convinced that the elec- 

 tricity manifested in an insulated boiler, during the emission 

 of steam, could not be attributed to the accompanying eva- 

 poration of the water ; and being wholly unable to conceive 

 any other cause, operating in the boiler, to which the effect 

 could with any probability be ascribed, I became persuaded 

 that the source of the electricity could only be situated at 

 the discharging orifice, or in the channel through which the 

 steam was conveyed to it. Such of my previous experiments 

 as appeared to militate against this supposition, I conceived 

 might probably have been rendered fallacious by the omission 

 of proper precautions to prevent a conduction of electricity, 

 by moisture, between parts of the apparatus which I had as- 

 sumed to be insulated, with respect to each other. I there- 

 fore determined to repeat the principal experiment of this 

 kind, with the addition of such measures as I deemed re- 

 quisite, to obviate the defect I have alluded to, and the fol- 

 lowing is the mode in which I proceeded. 



Into an insulated boiler I inserted one end of the glass 

 tube A, which was placed in a horizontal position, and to the 

 other extremity of which a stop-cock C was affixed, having 

 a passage through it considerably smaller than that through 

 the tube ; and in order to prevent any communication of elec- 

 tricity between the boiler and the cock by the deposition of 

 moisture on the inner surface of the glass, I surrounded part 

 of the tube with a red-hot iron cylinder, which is represented 

 at B. I then attached to the cock a second glass tube D, 

 from the extremity of which the steam was discharged. 



Upon opening the cock the ejected steam proved, as usual, 

 to be positively electrified ; but the boiler, which in all former 

 experiments had yielded the opposite electricity to that of the 

 steam-cloud, now remai7ied neuter; and the cock, instead of 

 the boiler, became negatively electrified. When I say that 

 the boiler remained neuter, I must be understood to mean, 

 that it was as nearly so as could be expected from the diffi- 

 culty of wholly intercepting the transmission of electricity 

 from the cock to the boilei". Feeble electricity did appear 

 in the boiler, but no question could exist with respect to its 

 origin ; for when I touched the cock with a wire, the electri- 

 city of the boiler vanished entirely; but when I touched the 

 boiler, the electricity of the cock was scarcely diminished ; 

 and upon forming a communication between the boiler and 



