of Radioactive .Products present in the Atmosphere. 839 



We see that the ratio and the wind velocity arrange them- 

 selves practically in the same order. 



Consequently, the relative ionization of the thorium and 

 the radium types depends on the height at which the wire 

 has been stretched. 



Summary of the Results. 



(a) The decay curves show that the particles of radium A 

 and thorium A are deposited on a negatively charged wire 

 but not other products, such as radium B, radium C, &c. 



(h) According to the theory put forward, the number of 

 the particles of radium A deposited per second on unit length 

 of the wire should be a definite quantity, depending on the 

 mobility of the particles, the height of the wire above the 

 ground and its charge per unit length, bnt not on the velocity 

 of wind, if its component perpendicular to the length of the 

 wire is greater than a certain value. 



(c) If the mobility of the particles of radium A be sup- 

 posed to be constant and equal to 1*3, the average amount 

 of the radium emanation present in the atmosphere at Tokyo 

 should be about 



5x 10 ~ 12 curie per cubic metre. 



(d) On the assumption that the amount of the thorium 

 emanation per unit volume is the same at equal heights, the 

 ratio of the amount of the radium emanation to that of the 

 thorium is estimated to be 



13,000 : 1, in the vicinity of the height of 6*5 metres 

 above the ground, on the average, and 

 (5,500 : 1, in that of the height of 1*5 metres. 



(e) When we compare the amount of the radium emana- 

 tion thus obtained with those found at Montreal, Chicago, 

 and Cambridge, we find that the former is much smaller 

 than the latter. If the actual amount of the emanation at 

 this locality be of the same order as that at the places just 

 referred to, we should suppose that the particles of radium A 

 become, while suspending in the atmosphere, heavier particles 

 at a rate much quicker than that at which they are transformed 

 into atoms of radium B. 



(/) If this is the case, the ratio given in (d) becomes 



47,000 : 1, in the vicinity of the height of 6*5 metres 



above the ground, and 

 24,000 : 1, in that of the height of 1*5 metres. 



(</) A fall in atmospheric pressure seems to have the tendencv 



3K2 



