al 
through Oxygen and Hydrogen at Low Pressures. 2295 
pressure by means of another stopcock K which it carried. 
When this was done, K was closed, and atter the pressure yg 
Fig. 2. 
(\ 
S a 
iy ih 
R= } 
A 
yy Ar=+B 
Ny 
IES MAAR SASS SAAN Rasa 
SSSA ASAIN SA hs 

aa. 
within the volume to be measured had been determined through 
the manometer, the stopcock S was opened. The pressure then 
rose, say, to p. Then the volume sought was (II denoting 
CT SSMS SSS SSS Soe oe Me 

atmospheric pressure) ae times the volume of the bulb, 
m0 
by Boyle’s and Avogadro’s laws. The volume of the bulb 
was found by filling it with water and weighing the water. 
In this way the required volume of the apparatus cut off by 
the stopcocks was found with sufficient accuracy to be 570 e.c. 
In order to test the effect of the passage throngh the mixed 
gases of small currents unattended by sparking, the upper 
plate ZN was put in metallic connexion with an electrometer. 
AB was then charged to any required potential by connecting 
it to the positive end of a battery, the negative end of which 
was earthed. Meanwhile, of course, ZN and the electro- 
meter were earthed. After the electric force between the 
plates was established, the quadrants connected to ZN were 
insulated, and the electrometer gave no deflexion until the 
ultra-violet light was turned on. When the light was started, 
the magnitude of the current through the gas was exhibited 
by the motion of the electrometer-needle. Prof. Townsend 
has shown (Phil. Mag. Feb. 1901, and subsequent papers) 
Phil. Mag. 8. 6. Vol. 7. No. 38. Feb. 1904. Q 
