1895.] On the Diselectrification of A ir. 437 



tion by bubbling, and for collecting large quantities of electrified 

 air. 



2. In fig. 1 , A B represent the two terminals of a Yoss electric 

 machine connected, one of them to a metal can, CO' (a small biscuit 

 canister of tinned iron), and the other to a fine needle, of which the 

 point n is in the centre of the can. The wire making the connection 

 to the needle passes through the centre of a hole in the side of the 

 can, stopped by a paraffin plug. Air is blown from bellows through 

 a pipe, E, near the bottom of the can, and allowed to escape from 

 near the top through an electric filter, F, called the tested filter, 

 from which it passes through a long block-tin pipe, GGr, about 

 3 j metres long and 1 cm. internal diameter, and thence through a 

 short tunnel in a block of paraffin, K. From this, lastly, it passes 

 through a second electric filter, B, into the open air. This second 

 filter, which we sometimes call the testing filter, sometimes the electric 

 receiver, is kept in metallic connection with the insulated terminal, I, 

 of a quadrant electrometer, Q. The metal can and the block-tin 

 pipe are metallically connected to the outer case and uninsulated 

 terminal, T, of the quadrant electrometer. 



3. The testing filter or electric receiver consists of twelve discs 

 of brass- wire cloth fixed across the mouth of a short metal pipe 

 supported on the end of the paraffin tunnel in the manner represented 

 in fig. 2, on a scale of twice the size of the filter which we have 

 actually used, or of true size for a filter on a tube of 2 cm. diameter, 

 which for some purposes may be better. One of eleven similar discs, 

 of size adapted to a tube of 2 cm. diameter, and an outermost disc 

 with projecting lugs, are shown, true size, and with the gauge of the 

 wire-cloth which we have actually used, shown true size, in fig. 3. 

 The eleven little circular discs of wire cloth are held in position by 

 bending over them the four lugs belonging to the outermost disc, and 

 all are kept compactly together by a short piece of india-rubber tube 

 stretched over them outside as shown in fig. 2. 



4. We commenced with a few experiments to test the efficiency of 

 the testing filter, R, with no tested filter at F, and merely continuous 

 block-tin pipe, FGG, from the can to the paraffin tunnel. First, 

 working the bellows with no electrification of the needle point, we 

 found no sensible electric effect on the electrometer, which proved 

 that, whether from natural electrification of the air of the laboratory, 

 or by the action of the bellows, or by the passage of the air through 

 the long metal pipe, no electrification sensible to our test was pro- 

 duced. After that we kept the needle point, n, electrified, either 

 positively or negatively, for five or six minutes at a time by turning 

 the little Voss machine, and we found large effects rising to about 

 3J volts in five minutes, positive or negative, according as n was 

 positive or negative. 



