8 NUCLEATION OF THE UNCONTAMINATED ATMOSPHERE. 



coronas. Nuclei originating or lost at the left-hand end of the cham- 

 ber will additionally distort the corona, and such distortion is clearly 

 in evidence, apart from the one-sided position of the coronas. 



Mere inspection of the coronas (figs. 2-6) shows that they are larger 

 for fog particles near the axis, and smaller for particles near the top 

 and bottom of the condensation chamber. Hence it is next necessary 

 to explain that the details of the distorted coronas observed actually 

 correspond with a gradation of the number of effective or available 

 nuclei, from the axis outward on all sides. In the case of linearly 

 graded fog particles increasing in diameter, 8, from bottom to top, it 

 appears that the equation of the apertures, s, of the loci* of like color 

 of the corona is 



2 a s sin <6 



~ _^_ ** T ' ' 



a sin 



where s is the aperture for the particles of diameter, S , in the horizon 

 or plane of sight, and 8 the angle in polar coordinates between the 

 radius vector to the part of the corona in question and the horizon- 

 tal, the origin being at the center of the corona. Finally 8 = 8 ah. 

 Such coronas when the gradation becomes marked are campanulate 

 in outline, finally becoming basin-shaped. 



FIG. j. Computed curves. 



In the present case, however, there are two symmetrical distribu- 

 tions of this kind, i. ?., increasing diameters of fog particles from 

 the axis of the chamber toward the top and the bottom. Hence 

 pairs of intersecting curves, two examples of which are given in 

 figure j (a' > a), show the coronas to be anticipated, if the remote 

 parts beyond b and c of the corona are ignored and only the stronger 

 curves surrounding the spot of light, d, admitted. In other words, 



*Barus: Am. Journ. Sci. (4), XIII, p. 309, 1902. 



