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XXI. The Effect of the Passage of Electricity through a 
Mixture of Oxygen and Hydrogen at Low Pressures. By 
Rey. P. J. Krrxpy, Fellow of New College, Oxford *. 
fe object of these experiments was to examine the 
chemical action attending the passage of electricity 
through a mixture of hydrogen and oxygen. 
The apparatus was designed with the view of ascertaining 
whether chemical combination is produced by a small current 
unaccompanied by sparking. It was also used for larger 
eurrents attended by a spark and glow in the gas. 
It was proposed to produce the small currents by the 
motion under an electric force of ions set free by the action 
of ultra-violet light on a zinc plate. 
The essential part of the apparatus accordingly consisted 
of two parallel metallic plates, the upper, the zine plate ZN 
(fig. 1), being within an air-tight bell-jar which was fastened 
to, and rested upon, the lower, a brass plate AB. Their 
distance apart was nearly 1 cm.—more precisely 9°77 mm. A 
cireular hole was turned out of the centre of AB to allow 
the passage of the ultra-violet light into the apparatus, and 
Fig. 1, 

over the hole and beneath the plate was fastened the quartz 
plate Q. The continuity of the upper surface of AB was 
* Communicated by Professor Townsend, F.R.S. 
