I860.] on Atmospheric Electricity. 283 



The burning match in the apparatus which has just been described, 

 performs the collecting function referred to above. The collector 

 employed for the station apparatus, whether the reflecting electrometer 

 or the common house electrometer is used, is an insulated vessel of 

 water, allowed to flow out in a fine stream through a small aperture 

 at the end of a pipe projecting to a distance of several feet from the 

 wall of the building in which the observations are made. 



The principle of collecting, whether by fire or by water, in the 

 observation of atmospheric electricity, was explained by the speaker 

 thus : — The earth's surface is, except at instants, always found elec- 

 trified, in general negatively, but sometimes positively. 



"If a large sheet of metal were laid on the earth in a perfectly 

 level district, and if a circular area of the same metal were laid upon 

 this sheet, and after the manner of Coulomb's proof plane, were lifted 

 by an insulated handle and removed to an electrometer within doors, a 

 measure of the earth's electrification, at the time, would be obtained ; 

 or, if a ball, placed on the top of a conducting rod in the open air, 

 were lifted from that position by an insulating support, and carried to 

 an electrometer within doors, we should also have, on precisely the 

 same principle, a measure of the earth's electrification at the time. 

 If the height of the ball in this second plan were equal to one-sixteenth 

 of the circumference of the disc used in the first plan, the electrometric 

 indications would be the same, provided the diameter of the ball is 

 small, in comparison with the height to which it is raised in the air, 

 and the electrostatic capacity of the electrometer is small enough not 

 to take any considerable proportion of the electricity from the ball in 

 its application. The idea of experimenting by means of a disc laid flat 

 on the earth, is merely suggested for the sake of illustration, and 

 would obviously be most inconvenient in practice. On the other hand, 

 the method by a carrier ball, instead of a proof plane, is precisely the 

 method by which, on a small scale, Faraday investigated the distribu- 

 tion of electricity induced on the earth's surface, by a piece of rubbed 

 shellac ; and the same method, applied on a suitable scale for testing 

 the natural electrification of the earth in the open air, has given in the 

 hands of Delmann, of Creuznach, the most accurate results hitherto 

 published in the way of electro-meteorological observation. If, now, 

 we conceive an elevated conductor first belonging to the earth, to 

 become insulated and to be made to throw off" and to continue throwing 

 off portions from an exposed position of its own surface, this part of its 

 surface will quickly be reduced to a state of no electrification, and the 

 whole conductor will be brought to such a potential as will allow it to 

 remain in electrical equilibrium in the air with that portion of its 

 surface neutral. In other words, the potential throughout the insu- 

 lated conductor is brought to be the same as that of the particular 

 equi-potential surface in the air, which passes through the point of 

 it from which matter breaks away. A flame, or the heated gas 

 passing from a burning match, does precisely this : the flame itself, or 

 the highly heated gas close to the match, being a conductor which is 



