Manchester Memoirs, Vol. xlviii. {\(^o/\^, No.\%. 



XII. On the rate at which Ions are generated in the 

 Atmosphere. 



By Arthur Schuster, Ph.D., F.R.S. 



Received and Read March ist, igo^. 



Two methods of measuring the ionization of the 

 atmosphere are at present available. In the original 

 experiments of Elster and Geitel, the dissipation of the 

 electric charge of an insulated body was measured and 

 the results obtained under different atmospheric con- 

 ditions shewed that a closer investigation of the subject 

 might lead to conclusions of considerable importance. 

 But the dissipation of the charge of the electrified body 

 depends on a variety of circumstances, and the observed 

 changes in its amount are not easily interpreted. The 

 second method devised by Ebert aims at measuring 

 directly the number of ions in the air. Roughly speaking, 

 these amount under ordinary conditions, and for each 

 kind, to between two and four thousand per cubic 

 centimetre. The positive and negative ions are always 

 recombining, and if the total number remains approxi- 

 mately constant, this can only be due to the fact that a 

 continuous process of regeneration is going on at the same 

 time. Equilibrium is reached when the number generated 

 equals the number recombining in the same time. The 

 rate of recombination is found to depend on the amount 

 of dust with which the air is charged, and also apparently 

 on its humidity. If on a particular day, the number of ions 

 is found to be particularly large, this may be because 

 the rate of recombination is exceptionally slow, or the 

 regeneration exceptionally quick. None of the measure- 

 ments which so far have been carried out, attempt to 

 decide between the two alternatives, and yet this is perhaps 

 the most important question of all. 



March 26th, igo4. 



