276 Scientific Proceedings, Royal Dublin Society. 
Comte de la Baume Pluvinel had his various photographic 
cameras arranged to have photographic actions varying in such a 
manner that the greatest was 1000 times that of the least.. He 
finds, as a general result, that the best all-round negative is 
given by a photographic action equal to 4: but this does not 
agree with the results obtained in Chili and Brazil. A probable 
explanation is, that whereas in Chili and Brazil the sky round 
the corona was perfectly clear during totality, at Fundium 
there was light haze in the sky. M. Deslandres says there were 
‘*faint clouds,” and these would necessarily be illuminated by 
the corona, and would give a far brighter sky than was found in 
Chili and Brazil. Comte de la Baume Pluvinel, at Salut Isles, in 
1889, Dec. 21-22, found, using photographic actions varying 
from 185 to 18, that the best result was given with an action over 
13 and under 82, this agreeing very nearly with the results found 
by Professor Schoeberle and myself in 1893. I have at present 
no precise details of Professor Pickering’s exposures, and so cannot 
get his photographic actions, but the comparison of his results 
with those of Professor Schosberle and myself will be extremely 
interesting in settling this important point. 
There can be little doubt that the idea that long exposures 
and great photographic action are necessary for the external por- 
tions of the corona must be abandoned; and in devising instru- 
ments for future eclipses, there is nothing to be gained in this 
direction by the use of photographic actions exceeding 15 or 16. 
This will enable instruments of much greater focal length to be 
used for future work. An instrument working at a yo will 
secure all the external corona in about 15 or 16 seconds, and 
one at a zs will secure everything in about 100 seconds. 
In addition to a lens working at this ratio I would recommend 
the use of a 12-inch object-glass of 40, 50, or 60 feet focus, which 
would enable pictures of the corona to be obtained on such a scale that 
the image of the moon would be over 4, 5, or 6 inchesin diameter. 
Short exposures with this would give the inner and middle corona 
with all the beauty and delicacy obtained by Professor Schceberle 
in Chili; and 100 seconds’ exposure would give nearly all the 
corona that is within reach of the photographic method of attack 
