UNILATERAL RADIATION. 



aperture are generally out of the question. Moreover, the first con- 

 densation is accompanied by turbulent displacement of fog particles 

 and the contents of the receiver are thoroughly stirred up. After 

 filling with filtered air and exhausting again, the coronas are there- 

 fore nearly uniform and alike on both sides. In the above table the 

 nucleation produced decreases about as the inverse square of dis- 

 tance, but as the bulb is essentially variable in intensity such a result 

 is not trustworthy. 



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 at 

 X 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 (about si 30) of the coronas were 

 measured with two goniometers, 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 thousands per cm. 3 . 



diameter, <t> = s/$o. 



= 17 cm.; angular 



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. The smaller particles are therefore evaporated into water 

 nuclei (as will be shown below), while the initial temperature of the 

 fog chamber is being rapidly regained. 



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 : i , or in a larger ratio, 



