of observing contacts at the Sun’s limb. 375 
slit ; and the longitudinal line of demarcation, before referred 
to, between the brilliant and dusky portions of the spectrum 
was hard and sharp, in striking contrast with the effect of the 
sun’s limb, which under similar circumstances always gives a 
boundary more or less hazy and indefinite, and this to a degree 
continually changing from minute to minute. This contrast 
was beautifully exhibited a few seconds before the totality when 
the limbs of both sun and moon were on the spectrum together, 
the width of the visible portion of the sun having become less 
than the length of the slit. It was at first thought that this 
appearance was decisive against the existence of a lunar atmos- 
phere however rare: but a little consideration shows that on 
no means equal to C and D, ; but attention was immediately 
arrested by the fact that, unlike them, it extended clear across 
the spectrum, and on moving the slit away from the protuber- 
ance it persisted, while D,, visible in the edge of the field, dis- 
appeared. Thus it was evident that* this line belonged, not to 
the spectrum of the protuberance, but to that of the corona, 
* On two or three occasions previously I had been very much surprised at not 
being able to detect this line in the m of unusually bright prominences. On 
‘the d I once found it very easy to see at a place on the sun’s limb where 
the other chromosphere lines, usually far more brilliant, were almost invisible. 
