SECONDARY GENERATION. 69 



distances D= 10 to 26 cm. form a prolongation of the series, showing 

 further reduced fog limits and the probability of a doubly inflected 

 curve of the same type throughout. 



As a whole these observations corroborate what has already been 

 inferred, that nuclei of all sizes are present simultaneously ; that by 

 far the greater number have a size depending on the density of the 

 ionized field by which they are produced. These nuclei correspond 

 to the steeper ascent of the curves. With this given, the exception- 

 ally large nuclei at the lower end of the curve and the exceptionally 

 small nuclei at the upper end bring about the double inflection, since 

 the numbers of each gradually vanish. The more intense the ioniza- 

 tion, the more nearly are the nuclei of the same size, while for weak 

 ionization the gradation shown by the flat curves is accentuated. 



56. Secondary generation. In table 42 the endeavor was made to com- 

 pare the effects of the X-ray bulb acting to produce persistent nuclei 

 from different distances from the end of the fog chamber. Unfortu- 

 nately dense stratified fogs occur in the first exhaustion, which makes 

 it necessary to use the second exhaustion for the same nucleation as 

 a means of measurement. The pressure difference 8/> = 2o cm. is 

 below the fog limit, when air is not energized. 



The first two parts of the table show the rapid decrease of N with 

 increasing D ; but it is particularly remarkable that after the lapse of 

 2 minutes subsequently to the exposure, the nucleation (cat. par.} 

 has apparently increased (curves 74, 76), precisely as if there were 

 induced radio-activity in the nuclei, or in the apparatus, after the 

 X-radiation has been cut off. The incessant danger from undersatu- 

 ration is probably ineffective in view of the low-pressure difference. 

 It follows, then, that the decaying nucleus is radio-active (for which 

 reason probably the fleeting nuclei, though instantly generated, do 

 not decay at the same enormous rates), or that the larger nuclei break 

 up into smaller nuclei (increasing their number about threefold on the 

 average), or that small nuclei beyond the range of the exhaustion 

 gradually grow to a larger size. 



Special experiments to bring out this feature of secondary genera- 

 tion were made in table 42 and in the third, fourth, and fifth parts of 

 table 43. The phenomenon is put in evidence strongly on all cases, 

 but with an additional result, showing a tendency in the alternations 

 to disappear after several repetitions (curves 72, 73). The fifth part of 

 table 43 shows the occurrence of secondary generation even for dis- 

 tances of 20 cm. between the anticathode and the fog chamber. The 

 last datum is an indication of the growth of fog particles in the lapse 

 of time (curve 75). In the fourth part of table 43 (curve 72) the alter- 



