42 



Dr. H. H. Turner. On the 



any physical significance or not, is, at any rate, a convenient method of 

 expressing the facts. We may now turn to the measures previously 

 given of the 1893 corona,* and see how they accord with this formula. 

 On trial, it is found that a fair accordance can be secured if the con- 

 stant correction for sky-glare be taken as 2~ 7 ' s instead of 2~ 6 ' 4 , and the 

 constants for the four radii measured be 



N. S. E. W. Mean. 



-0-1 +0-4 +0-5 +0-1 +0-23 



16. With regard to the smaller value for sky-glare, if this depends 

 on the general brightness of the corona itself, we may remark that the 

 1893 corona was generally fainter, according to the measures, than the 

 1898 corona, the mean constant for the former being + 0*23, and for 

 the latter + 1*15. The difference is + 0'92, so that the 1898 corona 

 was about twice as bright, and hence twice as bright a sky illumination 

 is not unreasonable. 



Table II. — Comparison of Observed Brightness (Photographic) of 

 1893 Corona with the Law. 



Brightness x (distance from Sun's centre) 6 = constant. 



(The distances are given in units of the Sun's radius. The bright- 

 nesses are expressed by powers of 2 ; zero representing the Moon's 

 brightness.) 



Distance 



Typical 



With 

 " glare " 

 added. 



Observed error of formula. 



from 



brightness 











Sun's 

 centre. 



of corona 

 alone. 





S. 



E. 



W. 



1 -1 



^-0-2 



+ 0-2 





-0-9 







1-2 



-0-6 



-0-6 





-0 '4 







1 -3 



-1 -2 



-1-2 





-o-i 





+ 0-1 



14 



-1 -9 



-1 -9 



+ 0-4 



4 0-4 



-0-3 



+ 0-3 



1/5 



-25 



-25 



+ 0-2 



+ 0-4 





+ 0*5 



1-6 



-3 -0 



-2-9 



o-o 



+ 0-3 







1-7 



-3-fJ 



-3-5 



-o-i 



+ 0-4 





+ 03 



1 -8 



-4-1 



-4-0 



o-o 



+ -2 



+ 0-5 



+ 0-1 



1 '9 



-4-6 



-4'4 



-0-2 



+ o-i 





o-o 



2 -0 



-5-0 



-4-8 



-0-2 



-o-i 







2-1 



-5-4 



-5 2 



-0-2 



-0-2 





-0-3 



2 2 



-5-8 



-5 -5 



-o-i 



-0-2 



-0'2 



-0-7 



2-3 



-6-2 



-5-8 



-0'3 



-0-3 





o-o 



2 -4 



-6-6 



-6-1 



+ 0'2 



-o-i 







2 5 



-7-0 



-6 3 



+ o-i 



o-o 





o-o 



2 6 



-7 3 



-6-5 



+ 0-3 



o-o 



o-o 



+ o-i 



2 7 



-7-6 



-6-7 





+ o-i 





-o-i 



2-8 

 2-9 



-7-9 



-fi-8 



+ 0-3 



-o-i 







-8'2 



-7-0 





-o-i 





+ 0-1 



3-0 



-8'5 



-7-1 



+ 0-3 



-o-i 



o-o 



+ 0-1 



* ' Eoy. Soc. Proc.,' vol. 66, p. 403. 



