4 NUCLEATION OF THE UNCONTAMINATED ATMOSPHERE. 



while the ratio of distances is below 1:2, because the absorption of 

 the wood is equivalent to a removal of the bulb ; hence the density 

 of distribution falls off faster than the inverse cube. The contrast is 

 even greater, because in the 2 or 3 minutes of radiation some nuclea- 

 tion must arrive on the B side by convection and diffusion. 



We were originally of the opinion that there is marked absorption 

 of the nucleating power of X-rays, by the successive vertical layers 

 of air from left to right, but it is best not to prejudge the case here. 



5. Continued for larger pressure differences. Several questions now 

 present themselves for immediate decision, viz, whether all the X-ray 

 nuclei have been caught and in how far the exhaustions are below 

 the point of spontaneous condensation of moist air. Accordingly 

 larger pressure differences were applied. Table 3 gives a few examples. 



TABLE 3. Nucleations, n, in thousands per cm. 3 . Time of exposure to X-rays, 3.5 



minutes. Angular aperture < = .5/30. 

 5/= i 7 cm 2i cm 31 



.cm 



Side 



io~ 3 = 

 Ratio 



Hence above 8p = 21 cm. for this apparatus, nuclei show themselves 

 on both sides, and the question arises to what extent the normal air 

 nuclei (of dust-free air) have been captured. At &fi == 31 cm. the fog 

 particles condensed on X-ray nuclei probably drop out at once and 

 the persistent corona observed is precipitated on the normal air nuclei 

 stated. At all events, the gradual evanescence of the X-ray effect as 

 8p increases is noteworthy. 



6. Condensation dust-free of moist air in the absence of X-ray nuclei- 

 Fog limit. With the object of finding the pressure difference of 

 exhaustion, 8/>, corresponding to the lower limit of spontaneous 

 condensation of moist air without foreign nuclei, experiments were 

 first tried with a cock ^ inch in bore, in the exhaustion tube. The 

 results were identical on the A and the B sides, as follows : 



TABLE 4. Spontaneous condensation in saturated air. Angular aperture <f> = 5/30. 



dp - 24 cm 31 



5 = 2.2 2.7 



Repeated, s = 2.4 3.2 



" S- 2.1 



Do., large filter, s - 2.2 3.5 



Do. s = 1.9 



Air over night, s = 2.0 



5 /> = 22 cm , n == o 



