598 Prof. J. 8. Townsend on the Genesis of Tons 



from air which comes into contact with a conductor. To 

 show this the fan was placed within a large closed box 

 (50x80x140 cms.). B}^ means of an Ebert aspiration 

 apparatus the ionization of the air within the box was de- 

 termined before and after the fan had been set in motion. 

 The results showed a great decrease in the ionization as a 

 result of the air being continually driven into contact with 

 the walls of the box. Before the fan started 0*4 electrostatic 

 unit was found in a cubic metre of air ; after it had been in 

 motion ten minutes, and while it was still in motion, a 

 determination showed that this quantity had been reduced to 

 0*1. As far as the Ebert apparatus was able to show, its 

 accuracy not being greater than 5 per cent., there was the 

 same number of positive as negative ions in both experiments. 



Applying now these results to atmospheric electricity and 

 the earth's negative charge, it would be rash to say that they 

 disprove the theory of the permanent charge being due to 

 ion absorption, but they show that the process which Elster 

 and Geitel consider is taking place in the atmosphere is not 

 substantiated by experiment. We are also brought face to 

 face with the fact that as yet no conductor has been charged 

 through absorption of ions from the naturally ionized air of 

 the atmosphere (charging due to the volta effect being 

 excepted), and until this is done we cannot consider the 

 problem of the earth's negative charge as being solved by 

 the " absorption of ions from the atmosphere.'' 



In conclusion I would like to express my thanks to Prof. 

 AViechert for the helpful interest he has taken in this work, 

 and for placing every facility at my disposal for making 

 these experiments in the Geophysical Institute in Gottingen. 



LXXVI. The Genesis of Ions by the Motion of Positive 

 Ions in a Gas, a^id a Theory of the Sparking Potential, 

 By John S. Townsend, Wykeham Professor of Physics, 

 Oxford *. 



IN a paper published in the ' Electrician/ April 3, 1 903, 

 I gave an outline of a method by which some pro- 

 perties of positive ions may be investigated. The present 

 paper contains a fuller account of the theory of the genesis 

 of ions by positive ions and its application to experiments 

 which have been made with air and hydrogen. 



The theory is founded on the determinations of the con- 

 ductivity which takes place between parallel plate-electrodes 

 when ultra-violet light falls on the negative plate. 



* Comnumicated bv the Author. 



