EXPERIMENTS WITH IONIZED AIR. 



48 



^B, 



electrometer, whicli is thus at the same potential as the plate C. P is a i)hosphoru8 

 grid, consisting of two sheets of wire gauze placed close together facing each other, 

 so that between them discs of phosphorus may be secured. As the air has free 

 access to P on all sides, the medium between C and /' is heavily charged with 

 phosphorus "dust." The 

 essential precautious to be 

 pi-eserved in work of this 

 kind have been given else- 

 where. Barriers ai'e placed 

 for examination between C 

 and P, quite out of contact 

 with the former plate. 



The arrangement of 

 condenser selected is thus 

 essentially one in which the 

 air at P is saturated with 

 phosphorus emanation at 

 all times. On passing from 

 P to C this saturation is 

 reduced, depending on the ^TTTnTOkT 

 distance apart of the plates. Kx (l ' ' ' I ' '^ ' ' 

 The actual form of the con- 

 denser is shown in figure 2, 

 where i? is a hard rubber 

 base on which the plates 6' 

 P, are supi)orted on metal- 

 lic feet at a distance x apart. 

 They are secured by spring 

 terminals, a, h, adjusted by 

 clamp screws. The charg- 

 ing key has been drawn in 

 diagram in figure 1, where 



a, h, are parallel insulated metallic rods, trunnioned at c, d, and there put to earth 

 and connected with the condensers, respectively. The terminals of the charging 

 circuit are e and/. The level's are either top heavy or controlled by spi'ings to the 

 effect that contact with one side or the other is always made unless broken by 

 special adjustment. It is frequently difficult to keep these keys fi'ee from leakage, 

 so that simple devices are sometimes to be preferred. 



3. Co)nputation.—The com[)utation of the present results of discharge may be 

 made in the usual way. The curves are obviously nearly exponential. In other 

 words, initially, ^dV^cVcU, (/ F being the loss of potential in the time dt when 

 the potential difference of the plates is F, and c being a constant. Thus cF is 

 proportional to the cui'i'ent flowing l)etween the [)lates and F= F^f^'''-. The 

 constant c occurring in this equation has for the present either the meaning of 



Fig. 7. 



H 



^ 



Fig. 2. 



r 



B 



Fig. I. — Diagram of the Condenser and the Electrometer in 

 Parallel. Fig. 2,— Sectional Elevation of the Condenser. Scale, 

 1/6. Fig. 7.— Diagram. 



