C. Barus — Distribution of Nuclei. 



177 



exhausting again, the coronas are therefore nearly uniform and 

 alike on both sides. In the above table the nucleation pro- 

 duced decreases about as the inverse square of distance. 



4. Axial radiation entering one end of trough. — Seeing 

 that it is possible to retain the nuclei on one side of the trough, 

 subsequent experiments were conducted with the X-ray bulb 

 placed as shown in the figure. Moreover a smaller interval of 

 radiation was selected, to more and more fully exclude the 

 displacement of nuclei by diffusion. The angular diameters 

 (s/30) of the coronas were measured with two gonimeters, one 

 on each side (A and B) of the trough, the distance of the 

 coronal centers from the bulb being about 20 cm and 47 cm , 

 respectively. The following table summarizes the results 

 obtained, remembering that all initial coronas are coarse and 

 blurred and accompanied by copious rain and fog, so that the 

 diameters must be estimated. 



Table 2. — Number of nuclei 



in 



;housands per cm 3 . 



6p=V\ 



cm . 



ang 



ular diameter ty- 



=s/30. 



Time of radiation __ 



2 '5 min. 



3 '5 min. 



2 min. 



2 min. 









A-side 



B-side 



A-side 



B-side 



A-side 



B-side 



A-side 



B-side 



Corona on 1st exhaustion 



s 

 4-5 



n 

 32 



s j n 

 2-23-3 



4-5 



3-2 



n 

 32 

 11 



s n 

 2-23*3 

 3-09-3 



s 

 4-0 



n 

 22 



s 

 2-0 



n 

 2-5 



s 

 2-5 



n 

 5-2 



s n 

 



The second coronas are obtained after refilling with filtered 

 air and it is noteworthy that after the rains of the foggy first 

 coronas fall out (which they do rapidly), there are abundant 

 nuclei left for the next corona. As stated, the nuclei are now 

 uniformly distributed, and the coronas persistent, while in the 

 first exhaustion, apparently, certain larger particles captured 

 all the moisture and removed it in a rainy precipitate. 



It is to be observed moreover that the nucleations on the A 

 and the B sides in these cases are on the average as 9 : 1 or in 

 a larger ratio, 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 oil 

 faster than the inverse cube. The contrast is even greater, 

 because in the 2 or 3 minutes of radiation some nucleation 

 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 succes- 

 sive 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: 



