40 



'Dr. H. H. Turner. On the 







Correction 











to X. 



y- 





-2 







o-o 



- 2 







-3 







+ 0-1 



- 2 



9 



-4 







+ 0-2 



-3 



8 



-5 







+ 0-4 



-4 



6 



-6 







+ 0-8 



-5 



2 



- 7 







+ 1-3 



-5 



7 



-8 







+ 2-0 



-6 







13. The measures on the plates were then corrected — 



(a.) For the particular plate, as in § 10 ; 

 (b.) For the sky-glare, as in § 11 ; 



and compared with the curve 



brightness x (distance) — A 



to get the value of the constant A for each of the six radii measured. 

 As above explained, the curve used was a straight line, obtained by- 

 plotting log brightness as ordinate and log distance as abscissa. The 

 constants found for the six radii were as follows — adopting as unit of 

 brightness that of the moon (assumed 0*02 candle at 1 foot), and of 

 distance that of the sun's radius, so that the constants represent the 

 brightness of the corona at the sun's limb expressed in moons : — 



Kadius. N. IST.E. E. S. S.W. W. Mean. 



A = +0-4 +1-9 +1-7 0-0 +2-3 + 0'6 +1-15 



Thus at the sun's limb the corona is more than twice as bright as the 

 full moon on the average. 



14. Finally, the individual measures were compared with the adopted 

 law, with the following results. In the column " Typical Curve " the 

 calculated brightness is given for A = + 0*6, the actual figures for the 

 different streamers differing from this throughout by constants which 

 are easily inferred from the values of A given above. 



