1882.] Photographing the Solar Corona without an Eclipse. 413 



ance is certainly very corona-like, and I am disposed to think it 

 probable that it is really due to the corona." Professor Stokes's 

 opinion was formed from the appearance on the plates alone, and 

 without any knowledge of their orientation. 



I have since been allowed, through the kindness of Captain Abney, 

 to compare my plates with those taken of the corona in Egypt during 

 the eclipse of May last. Though the corona is undergoing doubtless 

 continual changes, there is reason to believe that the main features 

 would not have suffered much alteration between May 17th and 

 September 28th, when the last of my plates was taken. This com- 

 parison seems to leave no doubt that the object photographed on my 

 plate is the corona. The more prominent features of the outer 

 corona correspond in form and general orientation, and the inner 

 corona, which is more uniform in height and definite in outline, is 

 also very similar in my plates to its appearance in those taken during 

 the eclipse. 



Measures of the average height of the outer and of the inner corona 

 in relation to the diameter of the sun's image are the same in the 

 eclipse plates as they are in my plates taken here. 



There remains little doubt that by the method described in this 

 paper, under better conditions of climate, and especially at consider- 

 able elevations, the corona may be successfully photographed from 

 day to day with a definiteness which would allow of the study of the 

 changes which are doubtlessly always going on in it. By an adjust- 

 ment of the times of exposure, the inner or the outer corona could be 

 obtained as might be desired. It may be that by a somewhat greater 

 restriction of the range of refrangibility of the light which is allowed 

 to reach the plate, a still better result may be obtained. 



Plates might be prepared sensitive to a limited range of light, but 

 the rapid falling oif of the coronal light about H would make it 

 undesirable to endeavour to do without an absorptive screen. Lenses 

 properly corrected might be employed, but my experience shows that 

 excessive caution would have to be taken in respect of absolute clean- 

 ness of the surfaces and of some other points. There might be some 

 advantage in intercepting the direct light of the sun itself by placing 

 an opaque disk of the size of the sun's image upon the front surface of 

 the absorptive screen. Though for the reasons I have already stated 

 I did not attempt eye-observations, there seems no reason why with 

 suitable screens and under suitable atmospheric conditions the corona 

 should not be studied directly by the eye. There might be some 

 advantages in supplementing the photographic records by direct eye- 

 observations. I regret that the very few occasions on which it has 

 been possible to observe the sun has put it out of my power to make 

 further experiments in these and some other obvious directions. 



