4 ROUGH WAYS MADE SMOOTH. 



what would seem like the most satisfactory evidence that 

 the relation is real. I must ask him to believe, however, 

 that my purpose is to ascertain where the truth lies. 1 

 shall neither introduce any observation of the corona 

 because it seems specially favourable to the theory that the 

 corona sympathises with the photosphere, nor omit any, 

 because it seems definitely opposed to that theory. To 

 prevent any possibility of being unconsciously prejudiced, I 

 shall take a series of coronal observations collected together 

 by myself, on account of their intrinsic interest, several years 

 ago, when I had not in my thoughts any theory respecting 

 periodic changes in the corona the series, namely, which 

 is included in the sixth chapter of my treatise on the sun. 

 Each of these observations I shall consider in connection 

 with the known condition of the sun as to spots, and those 

 results which seem to bear clearly, whether favourably or 

 unfavourably, on the theory we are enquiring into, I shall 

 bring before the reader. 



Kepler, whose attention had been specially drawn to 

 the subject of the light seen round the sun during total 

 eclipse, by certain statements which Clavius had made re- 

 specting the eclipse of 1567, describes the eclipse of 1605 

 in the following terms : * The whole body of the sun was 

 completely covered for a short time, but around it there shone 

 a brilliant light of a reddish hue and uniform breadth, which 

 occupied a considerable portion of the heavens.' The 

 corona thus seen may fairly be assumed to have resembled 

 in extent that of 1871. A bright corona, reaching like that 

 seen during the eclipse of July 1878 to a height of only about 

 70,000 miles from the sun's surface, would certainly not 

 have been described by Kepler as occupying a considerable 

 portion of the heavens, for a height of 70,000 miles would 

 correspond only to about a twelfth of the sun's diameter ; 

 and a ring so narrow would be described very differently. 

 It seems, then, that in 1605 a corona was seen which corre- 

 sponded with that observed when the sun has had many 

 spots on his surface. Now we have no record of the con- 



