Radioactivity and Ionization of the Atmosphere. 72o 



Substituting the observed values of i, A, and u in this 

 equation, the value of N can be deduced. The value of X 

 was found to be variable both from hour to hour and day to 

 day. The following numbers illustrate a few of the results 

 obtained. 



-pv , Number of ions per 



a ' unit volume. 



Nov. 20. 1901 40 



„ 21 „ 30 



„ 23 „ 14 



n 27 „ 16 



30 „ 13 



•• 



The temperature of the air in most of these cases was 

 about -12° C, 



A bright clear dav was found to o-ive a greater value of N 

 than a dull day. 



A very similar apparatus has been employed by H. Ebert* 

 to determine the number of ions present in the air, only in 

 his experiments the air was drawn between concentric 

 cylinders, and an electroscope employed instead of an 

 electrometer. 



We see from the above results, that the number of ions 

 per unit volume in the air varies considerably, but on three 

 days was almost the same as the number produced per sec. 

 in a closed vessel. 



This is a surprisingly small number if we consider the outside 

 air to be ionized at the same rate as the air inside the closed 

 vessel ; for we have shown earlier in the paper, that in a 

 closed space the number of ions per c.c. increases to 50 times 

 the number produced per sec. before the rate of recombination 

 is equal to the rate of production. 



After making due allowance for the causes tending to 

 remove the ions, viz., the presence of dust and other particles 

 in the outside air, and the electric field between the upper 

 atmosphere and the earth, the number per unit volume is far 

 lower than would be expected. It is possible that the 

 spontaneous ionization of the air observed in closed vessels 

 may be due (in part at least) to a radiation continuously 

 emitted from the walls of the vessel. The spontaneous 

 ionization of the outside air may, on this view, be much 

 smaller than that observed in closed vessels, and the number 

 of ions present per unit volume correspondingly less. 



McGill Universitv, Montreal. 

 June 9th, 1902. 



* Phys. Zeit. No. 46, 1001. 



