672 Effect of Dust and Smoke on the Ionization of Air. 



Thus, the fumes decreased the ionization current in A and 

 increased it in B. 



With denser fumes the leaf of A could be kept almost at a 

 standstill, and B discharged with great rapidity. 



The fumes were next passed through lead pipes 5 mm. in 

 diameter and 10 metres long. There was a slight decrease 

 in the effect, but it was still easy to increase the motion of 

 the leaf of B from 3 D/m. without the fumes to 200 D/m. 

 with the fumes. 



The presence of an intense ionization agent, such as 14 mg. 

 of pure radium bromide, in the centre of the coils made very 

 slight difference to the ionization current due to the fumes. 

 Since obtaining these results, I have read a paper by 

 M. Broglie in the Journal de Physique, Dec. 1909, where he 

 has proved that this result may be anticipated theoretically, 

 and that the presence of radium or Rontgen rays, causing 

 small ions, will but slightly alter the number of charged 

 centres, which tends to attain a limiting value of about 10 

 per cent, of the total centres ; this seems to be the case even 

 with considerable variations of the intensity of the ionizing 

 rays. I am glad to find that my results are in general 

 agreement with his ingenious experiments and interesting 

 paper. 



Summary and Discussion. 



1. With a constant ionizing source, such as the y rays 

 from 14 mg. of radium bromide, and a constant air current 

 to the testing vessel, the number of ions detected is dependent 

 on the purity of the atmosphere as regards dust, smoke, mist, 

 or other centres, and was found to vary as much as 50 per 

 ce,nt. 



2. The apparent excess of positive over negative ions is 

 due partly to diffusion to the tubes traversed by the air, 

 partly perhaps to a real excess, but also to the fact that both 

 kinds of small ions, particularly the negative, rapidly combine 

 with particles of smoke, dust, or mist, and pass through the 

 testing vessel undetected. Hence, apparatus such as JSbert's 

 measures the physical purity of the air rather than the 

 intensity of the ionizing agents. 



In the summer of 190b', when forest fires were prevalent 

 in Canada, and the sun was somewhat obscured by smoke, 

 the number of ions per cm. 3 , measured by the Ebeit; instru- 

 ment, fell as low as 100, or about 10 per cent, of the normal. 

 On the other hand, the number of ions similarly measured 

 over the ocean in very clear weather has been found as high 

 as 1200 to 14C0. Now the amount of radioactive matter 







