F. H. Bigelow — Further Study of the Solar Corona. 353 



Take the typical formula for N and compute sin 2 = — . N. 



The angle d derived from this is the distance from the coronal 

 pole at which the observed rays have sprung up from the 

 surface of the sun The values may be slightly in error by 

 the small inaccuracy of the chosen a, but the changed projec- 

 tion resulting from this imperfection is not great. 



This table shows that the coronal rays have their bases in a 

 zone about 34 degrees from the coronal pole, the belt being 

 about ten degrees in width, but its maximum density at the 

 parallel of 34 degrees. The conclusion is drawn that there are 

 no visible rays in the neighborhood of the poles, and hence the 

 appearance of the corona is similar to that of the terrestrial 

 aurora. 



Position of the Coronal Poles. 



We find the location of the north and south poles of the 

 corona in the following way. 



Let r 1 & 1 represent the measured 

 coordinates of each point, with the 

 numerical suffix. 



a 1 = angle at pole of disk to the 

 point on the ray. 



p 1 = angular distance from pole of 

 disk to point. 



& z= angular distance from coronal 

 pole to point. 



r' = radius of spherical surface 

 through point. 



B = angle at coronal pole from 

 pole of disk to point. 



c = angular distance of coronal 

 pole from pole of disk. 



Then x, = r sin 6. 



N = 



y 1 = r x cos 0,. 

 z = x, tan a 



%7t sin 2 0. 



3 r 

 angle as computed. 



P = projection of coronal pole c 

 on a plane through the poles of 

 the ecliptic. 

 D x = cCj sec a x . 



tan », = — = tan sec a. 



y* 



r 2 = rc^sec^i + y! 2 . 

 , where r = 1 for typical N, and Q Q is the mean 



3r 

 sin s 0' = — .N. 



87T 



In the Spherical Triangle ABC we have given, a = 0', b =p x i 

 A = 90° — ^. 



Hence, sin B = sin p x cos oc x cosec 0'. 



. cos-J(A + B) ,. ... 



tani<! =c^f|A=B)- tan «' , ' + ''>- 



