EXPERIMENTS WITH THE DISPLACEMENT INTERFEROMETER. 91 



It is certain, moreover, that the first of these coronas is essentially the first 

 in order, inasmuch as no other corona can precede it. It would follow that 

 the reddish coronas first visible when white light is used would correspond to 

 particles (X = 63Xio~ 6 ), 



cm. 



or not below io~ 4 cm. in diameter. 



In a general way these conclusions agree with the datum estimated for the 

 axial colors of coronas, where axial yellow, corresponding to second green 

 coronas, was referred to particles of the order of size io 4 d = 2.2 cm. In both 

 cases the assumption is made, of course, that all nuclei are caught in the exhaus- 

 tion. In fig. 51 I have shown an attempt to regard the middle of the first 

 ring as the minimum corresponding to the disk, as the intensities alternate. 

 In the graph the abscissas denote the diameter of fog-particle in io~ 4 cm., 

 computed from the successive exhaustions. The ordinates of the curves a 



7 

 6 

 5 

 4 

 3 









/JO 





4- 



3456 

 FIG. 51. 



8 



then indicate the diameter of particle if the aperture 5 of the middle of the 

 first ring is taken in the equation d = 2/vCA/s; whereas the ordinates of b show 

 the diameter of particle, when the aperture is measured as far as the middle 

 of the dark zone between the disk and first ring; i.e., midway between the 

 edge of the disk and inner edge of the first ring. Clearly the curve b is prefera- 

 ble. As far as particles of the order of size d = 3 X io~ 4 both methods (curve 6) 

 agree within the errors of observation; but for particles less in diameter, the 

 data of the optical method are increasingly too large as the particles become 

 smaller. 



