DISTRIBUTION WITHIN FOG CHAMBER. 147 



and finally wedge-shaped forms, showing, therefore, continued sym- 

 metry about the middle horizontal plane or plane of vision, in spite of 

 the whirling rains and densely stratified fogs which accompany the 

 advanced condensations. The design lasts but an instant, for although 

 the nuclei may be suspended in accordance with the given distribution, 

 this is not possible for the heavy fog particles after condensation. 



These phenomena bear fundamentally on the origin of persistent 

 nuclei, and these are obviously graded in size, decreasing from the A 

 to the B sides, as well as from the middle plane toward the top and 

 bottom of the fog chamber. With regard to the latter or horizontal 

 symmetry, moreover, the distortion is such that the fog particles must 

 increase in size, from the plane of symmetry down and up. 



If the gradation is linear, for instance, with a coefficient, a, so that 

 dd^ah, where d is the diameter of fog particle at a height or a 

 depth, h, from the plane of sight, and s the radius vector from the 

 coronal center to a locus of uniform color, a, the angle of ^ with the 

 horizontal, 



s = (ay siii a) ( i j/i-r-2a.y sin a/</ ) . 



These curves are campauulate in outline, passing from closed roundish 

 to open basin-shaped forms, and two examples, a and a' ' , are shown in 

 figure 7, Chapter I. They all intersect at b and c, and the ends lying 

 outside these lines may obviously here be ignored. As the march 

 from a to a' is one of intensified gradation, the curves eventually 

 becoming flat, it is clear that the horizontal symmetry of figures 2 to 6 

 is suggested. The latter contain, in addition, the essential gradation 

 from left to right, due to the position of the bulb. 



J t 1 



10 <T. Origin of persistent X-ray nuclei. Admitting that the fog parti- 

 cles are larger from the middle plane toward the top and bottom of 

 the fog chamber, the nuclei must either be large in size toward the 

 top and bottom as well as toward the bulb, or they must be smaller in 

 number. The latter case may be dismissed. It follows, then, that the 

 layers of stagnant, originally dust-free, air within the chamber become 

 more and more rich in relatively large nuclei as they lie nearer the 

 top and bottom and the end. (The corresponding effect toward and 

 from the line of sight will, of course, remain invisible.) These large 

 nuclei capture nearly all the moisture in the parts in question, giving 

 rise to the whirling rains and dense fogs after condensation, whereby 

 the essentially unstable character of this distribution is made manifest. 



Hence the case is such as if the persistent nuclei were generated by 

 the impact of the X-rays of sufficient intensity on solid and liquid parts 



