1871J The Eclipse of Last December, 241 



Fellow of St. John's College, Cambridge, referring (at the 

 January meeting of the Royal Astronomical Society) to 

 the V-shaped gap exhibited in Lieutenant Brown's drawing 

 (of which figure 9 is a reduced outline-view) remarked that 

 the gap appeared to him somewhat larger ; and Lieutenant 

 Brown agreed that his drawing did not quite adequately 

 represent the dimensions of the gap. 



So far, then, the evidence is most satisfactory. It may be 

 indeed regarded as already sufficient ; since no peculiarity 

 of our own atmosphere could possibly explain the similarity 

 of the views seen at stations so far apart ; while the fixity 

 of the gap, a fixity respecting which all accounts agree, 

 disposes of the theory (untenable also on other accounts), 

 that the bounding radiations which formed the gap were due 

 to matter near the moon illuminated by the solar rays. 



But Lord Lindsay, and Mr. Willard (a member of the 

 American observing party), had photographed the eclipse at 

 stations nearXeres; and here was a further means of testing 

 the matter. If the photographs showed the V-shaped gap, 

 the evidence would indeed be irresistible. 



Now, as respects Lord Lindsay's photographs, 1 am able 

 to say but little. He had with great spirit undertaken his 

 share of the observations at a time when it seemed likely 

 that Government aid would be refused altogether. He had 

 furthermore taken out at his own expense a fine 12^-inch 

 reflector by Browning. The ingenious contrivances by 

 which the production of the successive pictures was mecha- 

 nically provided for, enabled Lord Lindsay to take no less 

 than nine photographs. But those I have seen suggest the 

 belief that, so far as the corona is concerned, the results 

 would have been more satisfactory had fewer pictures been 

 taken, the exposure of each being correspondingly increased. 

 The very clearness with which, in a most beautiful photo- 

 graph of the series, now lying before me, the prominences 

 are shown, leads me to believe that the exposure was alto- 

 gether too short. We have evidence, both in the American 

 photograph and in that by Mr. Brothers, that the actinic 

 energy of the prominence light is much greater than that of 

 the corona, " the light of which," says Mr. Brothers, in 

 a letter to me, "rather resembles moonlight in this respect." 

 A photograph, therefore, which shows the corona well 

 cannot possibly show the prominences clearly — though the 

 effects of the prominences may be very marked indeed ; and, 

 vice versa, a. picture in which the prominences are well- 

 defined cannot be expected to show the details of the 

 corona. 



VOL. VIII. (O.S.)— VOL. I. (N.S.) 2 I 



