44 NUCLEATION OF THE UNCONTAMINATED ATMOSPHERE. 



definitely as follows: Let 8p be the fog limit of the given gas satu- 

 rated with moisture. Let S/>' > Bp be a pressure difference producing 

 strong coronas. Let S/>" <8/> produce no condensation at all in the 

 dust-free gas (below the fog limit). Then if the fog chamber is 

 exposed to radiation in a definite way, in a definite time, and thereafter 

 left without interference, 8/>' will produce coronas for hours after the 

 radiation ceases. If, however, immediately after the exposure S/>" is 

 applied, producing no condensation, and if (dust-free air being intro- 

 duced at once), without loss of time, p' is now applied, will coronas 

 appear or will they not appear in spite of the excessive exhaustion ? 

 In other words, has the nucleus returned to dust-free air? 



Thus, in table 25, experiment i shows that mere lapse of time has no 

 relatively important effect. In experiments 2 and 3, the first exhaus- 

 tion at S/> = i8 has all but destroyed the corona, for 8p = 2$ subse- 

 quently applied, which should, by experiment 3, have been s = j.o cm. 

 Similar remarks apply to experiment 4. Experiments 5 and 7 instance 

 the usual case, that if a corona is produced in the first exhaustion, there 

 will always be a smaller one in the second exhaustion. These are 

 the favorable experiments ; but experiment 6 and others which might 

 be added show that the effect of the lower exhaustion does not disrupt 

 the nucleus for the higher exhaustion . Thus there is no trustworthy 

 evidence for the flying to pieces of the nucleus, and, in fact, the next 

 section (table 27) shows that X-ray nuclei sustain high sudden exhaus- 

 tions without being dissipated or failing to produce condensation. 

 The difficulties encountered are without doubt referable to the vari- 

 ability in action of the X-ray bulb. 



TABLE 25. Possible rupture of the nucleus. 



*Spontaneous condensation. fThin drifting fog. 



Experiments were also made under satisfactory conditions with the 

 bulb at 80 cm. (table 26). But the nuclei so obtained are essentially 

 fleeting and would vanish without the first exhaustion. 



