223 
Proceedings of Royal Society of Edinburgh. [sess. 
illuminated by the setting sun. It looked like a vast sea over 
whose waves gravitation had ceased to hold sway, and whose waters 
were luminous with condensed sunshine. 
When the hill top began to emerge from the clouds and to be 
only occasionally covered with fog, as each fog mass cleared away 
to the east and let the sun shine on us, we saw our shadows cast by 
the setting sun on thej retreating bank of cloud, “ glories ” surround- 
ing the shadow-heads. Around the shadow of his head each 
observer saw a coloured halo ; near the shadow-head there was a 
small luminous but colourless halo, and round this a rainbow-like 
circle of colours, violet being inmost and red outside. When this 
coloured circle was brilliant another circle of colours immediately 
outside was seen, and having the colours in the same order as the 
first. 
After this display of colour in the east had come to an end, and 
no more clouds passed over the hill top, owing to the air being 
now clear to the west, an interesting display of colour took place 
in the west. At a point between the sun and the observer, there 
was a break in the cloud stratum, and the air seemed to be rising 
through this opening, and tearing the eastern edge of the cloud into 
fragments, which it carried from the dark shadow up into the sun- 
light. Here these fragments were rapidly dissolved in the dryer air 
above, and as they dissolved they gave rise in their dying moments 
to a brilliant display of opalescent colours, the different parts of 
the vanishing fragments taking on the most brilliant colours, and 
changing from one colour to another, and then vanishing so quickly 
that it was impossible mentally to follow the rapid display. 
The display of opalescent colours in the sky has been commented 
on a good deal during the last few years, and Professor Tait has, I 
think, remarked that it must take place oftener than is imagined. 
There does seem to be a probability of it occurring often, but the 
conditions necessary for the eye perceiving it do not seem to be 
frequent. On this occasion the colours were seen against a dark 
background, formed by the shadowed eastern edge of the cloud. 
These colours were seen near the sun, at only a small angle from 
it, and it would appear they are produced in the same way as the 
colours in halos seen round the sun. In experimenting artificially 
with these halos, it may be observed that the particular colour does 
