DECAY OF IONS. 



95 



63. Decay curve. Assuming that the rate of decay in the lapse of 

 time (t) is as the square of the number, or that i jni /n' = b (t-t f ) 

 where 6 is constant, a few incidental attempts were made to compute b. 



Table 38 and fig. 48 contain an example of such results, obtained 

 by exhausting the fog chamber at a stated time after the removal of 

 radium. The drop in pressure is below the coronal fog limit of air and 

 all precipitation takes place on ions. 



FIG. 



48 





10 



20 



30 



40 



50 



60 



10 



80 



90 



100 



Fig. 48. Decay of ionized nuclei (w per cubic centimeter) produced by 

 radium in dust-free air, in the lapse of seconds. Table 38. 



Table 38. Decay curve at 

 dp =23. Radium on top. 



For the first five seconds 6 = 0.0019, for 

 the first fifteen seconds 6 = 0.0022, etc., 

 the values obtained ranging from 0.002 to 

 0.003. This is larger than the electrical 

 datum 0.0014. Decay is more rapid than 

 the equation warrants. Initial coronas are 

 too large, final coronas too small, in spite 

 of the presence of air nuclei, the number 

 of which should be deducted at least in 

 part. Other experiments show similar co- 

 efficients. Thus the low curve of Miss Jos- 

 lin would conform to 6 = 0.0023. Natu- 

 rally the present method for 6 is much 

 inferior to the electrical method, even if 

 the two coefficients are identical ; but the 6 here is obtained under pos- 

 sible complications with the larger gradations of the colloidal nuclei of 

 dust-free air, though these are probably inefficient. 



If the values of i/n be inserted, the curves should be linear, since i/w 

 = z/n + bt, where t is the time dated since the occurrence of n . The 

 line passing through the observations at 5, 30, 50 seconds is best adapted 

 to represent the results, and compatibly therewith 6=0.0024 (n in 

 thousands of nuclei per cubic centimeter) may be roughly assumed. 

 These computed values of n are given in table 38 and shown in the chart 

 (fig. 48). They are too low initially and too high finally, even if the air 









