Dust and Smoke on the Ionization of Air. 6(>7 



obtained are shown in curve I., fig. 3. It will be seen that a 

 very large potential on T does not withdraw the ions, which 

 are, however, detected at B, although the potential is lower. 

 Without the flame curve II. was obtained. 



When the radium was removed from the room, similar 

 results were obtained when the gas was burning, but the 

 initial value for zero potential on T was less. 



Potential on T 



volts). 



Div 



./uiin. at B. 











4-0 



1500 







3-0 



2000 







2-4 



3000 







2-1 



4000 







1-9 



5000 







1-9 



The whole room contained a large number of the slow- 

 moving ions due to the flame, only a few minutes after 

 shutting the windows and lighting the Bunsen burner. 



Over a large city the contribution to the supply of large 

 ions, but slightly mobile and slow to recombine, by fires, 

 furnaces, flames, and smoke, must be considerable, and this 

 fact may help to account for the discrepancies among different 

 observers in their determinations of the number of large ions. 



With the windows open, without flame, smoke, or radium 

 in the room, the " natural ionization " in the Physics Building- 

 gave about 0*4 D/m, and it has been found that this is 

 equivalent to about 3000 ions per c.c. ; we can, therefore, 

 determine approximately the number of ions detected at B 

 under the conditions of the experiments. 



Div./min. No. of ions per cm 3 . 



Natural ionization 0*4 3,000 



Flame 4*0 30,000 



Radium, clear weather. . . 20'0 150,000 



„ smoke and mist 11*0 80,000 



artificial fog ... 9*0 70,000 



There was an essential difference between the natural 

 smoke and mist entering the window and that made artifi- 

 cially by flame, in that the ions due to the natural fog were 

 mainly removable by a moderate potential on T ; not so for 

 the artificial fog. 1 attribute this to the very large persistent 

 ions due to the flame. 



It may be worth recording that, in order to determine the 



