Mzxrson.—On the recent Sun-glows. 875 
One mountain, St. Augustine, was split into two parts; another 12,000 feet 
high was very violent—threw the whole district into darkness for some time 
and covered every foot of the ground to a long distance with a layer of ashes 
five or six feet deep. An island a mile and a half long and 75 feet high 
was suddenly formed, and tidal-waves 80 feet high broke on all the surround- 
ing coasts. Still even this was vasily inferior to the Krakatoa catastrophe, 
and almost all the prominent scientific men of the day concur in conuecting 
our sun-glows with the latter event, although they allow that the smaller 
eruptions of the year may have contributed to the intensity and duration of 
the displays. 
But it remains to be shown how that connection is established. Some- 
thing unusual was evidently carried into the higher air in immense quan- 
tities in the last days of August, 1883. What was that something ? Dust, 
vapour subsequently to be frozen into ice-erystals by the cold aerial upper 
currents, or some gas such as hydrogen or chlorine. Each of these has its 
advocates—perhaps the truth is that each has contributed to the result. 
Let us see more closely what is or can be advanced in favour of each 
supposition. 
Firstly, as to the hydrogen gas there really is little to say. Several 
authorities (Ellery and Hazen, e.g.) incidentally mention it as a possible 
product of the eruption, resulting from the decomposition of the ejected 
water through electric action, I suppose. When once released the hydrogen 
would readily and naturally ascend to a great height, for its specific gravity 
is less than that of any other gas, and we can conceive it as suspended at a 
great altitude in great quantities, and for a long time. But granting all 
this, would it produce the sun-glows? Mr. Ellery thinks not, and nobody 
of scientific standing contradicts him. Again the heavy yellow gas— 
chlorine—would probably be liberated in large quantities by the pouring of 
sea-water into the fiery craters of Krakatoa, and in combination with other 
causes may have contributed to the exceptional colouring. 
Secondly, there is the aqueous vapour, or rather ice-crystal theory. 
There is more to be said here. But, on the threshold, there is a great 
difficulty. Aqueous vapour in the air is no unusual thing. Often the 
atmosphere is heavily charged with it. But the sun-glows are phenomenal, 
Is it not curious that the vapour has never before assumed the condition 
requisite for producing such an effect? Hazen argues in favour of this 
theory thus: there are three conditions necessary to produce the best 
results in the way of sun-glows: (1) clear sky; (2) abundant refracting 
material; and (3) great force to carry the same high up into the air; all 
these conditions have been fulfilled. The universality of water secures the 
fulfilment of the second condition even independently of the Krakatoa 
