136 Proceedings of Boy at Society of Edinburgh, [jan. 30 , 
what appeared to be a peculiar pillar-like cloud, lit up with the light 
of the setting sun. What specially attracted my attention was that 
the streak of illumination was vertical, and not the usual horizontal 
band-form we are accustomed to. I looked in the direction of the 
sun to see if I could trace any peculiar opening in the clouds 
through which the light passed, but failed to do so. 
I continued observing for some time the peculiar appearance, 
when at last the pillar-like illumination became more elevated, 
and by the time the sun was just setting and I had arrived on the 
high ground, it had reached to a considerable height, and I at last 
began to suspect that what I had been looking at was not a cloud 
at all, but the “ tooth ” of a rainbow. Soon all doubt was put at 
rest by the red pillar extending, curving over and forming a perfect 
arch across the north-east sky. 
The rainbow when fully developed was the most extraordinary 
one I ever saw. There was no colour in it but red ; it consisted 
simply of a red arch, and even the red had a sameness about it ; all 
the other colours were absent. Perhaps this is stating it too 
strongly, as after careful observation I succeeded in detecting at 
one or two points traces of yellow; but of green, blue, or violet 
there was not a vestige, and in their place there was a dark 
band extending inwards to about the breadth usually occupied 
by these colours. This band, though distinctly darker than the 
sky, to the inside of it was not greatly so. Outside the rainbow 
there was part of a secondary bow, and inside, at certain places, 
there were indications of a supernumerary bow, as short detached 
red patches were visible at different points on the inner edge of the 
dark band. 
Por some time before the bow developed itself I had been watch- 
ing the Ochil Hills, which lay to the north of me. These hills at 
the time were covered with snow, and the setting sun was shining 
brightly on them. On many occasions I have seen snow-clad 
hills, in this and other countries, lit up with the light of the setting 
sun, and glowing with rosy light, but never have I seen such a 
depth of colour as on this occasion. It was not a rosy red, but 
a deep furnacy red. How, why was the colour on the hills of 
so deep a red on this evening? The monochromatic rainbow 
gives its own explanation; it also tells us why the hills glowed 
