470 Eclipse of the Sun in 1886 observed at Grenada. [Dec. 16, 



On the day "before the eclipse I took a considerable number of 

 photographs for the first test. No similarity has yet been traced 

 between the form of the corona as obtained on these plates, and the 

 form of the trne corona as obtained during the total eclipse. 



During totality I had intended to carry out the following pro- 

 gramme : — During the first minute a photograph was to be taken with 

 the prismatic camera. After that four plates were to be exposed 

 with the coronagraph with the same length of exposure as that given 

 during sunlight. The exposure was given automatically by means of 

 a shatter, with an estimated length of between one-tenth and one- fifth 

 of a second. Besides these, two photographs were to be taken with 

 exposures of five and ten seconds respectively. 



The programme could not be carried out exactly. Immediately 

 after I had commenced exposing the prismatic camera, 1 looked up, 

 and found that the corona was covered by a light cloud. The sky 

 became clear again in about fifty seconds. I was anxious not to take 

 any other photographs at the same time for fear of vibration ; but as 

 nearly a minute had been lost something had to be sacrificed, and I 

 decided to take some of the photographs with the coronagraph before 

 putting the cap on the prismatic camera. I do not think that the 

 work has suffered in consequence, and at all events I obtained all the 

 plates I had intended to. As to the results, I am not yet in a position 

 to fully report on them. 



The photograph obtained with the prismatic camera shows several 

 images of the prominences, and it therefore gives every promise of 

 yielding good results when measured and examined. 



The five and ten second photographs of the corona show signs of a 

 slight vibration, but they will be useful for the inner part of the 

 corona. As my main object was to obtain instantaneous photographs, 

 these long exposure plates had to be obtained by working the auto- 

 matic shutter by hand ; it was this probably that caused the vibration. 



The instantaneous photographs of the corona when developed were 

 complete blanks, proving that the exposure was too short. It should, 

 however, be observed that this does not prove that the light of the 

 corona was insufficient to cause an appreciable effect on the plate if 

 combined with other light. More light energy is necessary to start 

 photographic action than is required to produce a visible difference 

 of shade when once the action is started. 



Many of the photographs taken during partial eclipse show what 

 may be described as a false corona, that is, an increase of density near 

 the sun and between the cusps, or in front of the moon. In none of 

 them can the moon be seen eclipsing the corona. 



The results, therefore, are adverse to the possibility of obtaining 

 photographs of the corona in sunlight ; it is, however, I consider by 

 no means proved that the method is impossible. But at present I am 



