W. Huggins— Photographing the Solar Corona. 127 
tered from the terrestrial atmosphere. It appeared to me by no 
means improbable that under these conditions the corona would 
be able so far to hold its own against the atmospheric glare, that 
the parts of the sky immediately about the sun where the cor- 
ona was present would be in some degree brighter than the 
adjoining parts where the atmospheric light alone was present. 
t was obvious, however, that in our climate and low down on 
the earth’s surface, even with the aid of suitable screens, the 
addition of the coronal light behind would be able to increase, 
but in a very small degree, the illumination of the sky at those 
ea where it was present. There was also a serious draw- 
ack from the circumstance that although this region of the 
Spectrum falls just within the range of vision, the sensitiveness 
of the eye for very small differences of illumination in this 
tegion near its limit of power is much less than in more favor- 
able parts of the spectrum, at least such is the case with my 
own eyes. ‘T'here was also another consideration of ee phe: 
) 
. 
the corona is an object of very complex form, and fall 
ences of illumination, and also the enormous advantage of fur- 
nishing a permanent record from an instantaneous exposure of 
the most complex forms. I have satisfied myself by some lab- 
oratory experiments that under suitable conditions of exposure 
and development a photographie plate can be made to record 
minute differences of illumination existing in different parts of 
a bright object, such as a sheet of drawing paper, which are so 
Subtle as to be at the very limit of the power of recognition of 
a trained eye, and even, as it appeared to me, of those which 
Surpags that limit, 
small plane 
ulum was brought to focus on the ground glass. The 
