ANNIVERSARY ADDRESS. 19 
No doubt you are aware that three explanations have been put 
forward to account for these remarkable appearances. The first 
is that they are due simply to water vapour at an unusual altitude. 
This, I think, must be set aside, for it is scarcely conceivable that 
the phenomena should be so rare were this the cause. The present 
generation has hitherto seen nothing similar, and there seems to 
be no distinct record of like appearances in former times, unless 
indeed the atmospheric phenomena of 1831 were of the same kind. 
It is true that Professor Piazzi Smyth and others aver that they 
observed like appearances some thirty years ago, but it appears to 
be generally admitted that the atmospheric phenomena referred to 
were connected with ordinary red sunsets, where the rich colour- 
ing is evidently produced by the action of the sun’s rays on water 
or ice in fine particles, and that the late appearances are of a 
different character; and even if it were conceded that in some 
one part of the earth water vapour might occupy an unusual 
position and produce unusual displays, is it at all probable that 
within a limited period a like condition of water-vapour should 
prevail over the whole earth, and continue for months ? 
The second, and apparently the most popular, explanation is 
that the wonderful decomposition and reflection of light has been 
caused by fine dust, emitted during the great eruption of Krakatoa 
in the end of August last year ; and the third hypothesis is the 
same in so far as dust is concerned, but differs in regard to the 
origin of the dust, accounting it to be of meteoric or cosmical 
origin, instead of an emission from a terrestrial centre. 
Now in favour of the volcanic origin we are informed that dust 
as actually collected from new-fallen snow at Madrid on Decem- 
ber 7, very similar in composition to dust that had fallen near 
Krakatoa. Volcanic dust (of a different character however) was 
also found in new-fallen snow at Philadelphia on January 22; and 
at Constantinople on December 2 there was a shower of a white — 
substance like snow, of saltish taste and soluble in water. On the 
previous night there had been a gorgeous display of colour, the 
crimson glow being visible an hour and a half after sunset, and 
