Meeson. — On the recent Sun-gloivs. 375 



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 30 feet high broke on all the surround- 

 ing coasts. Still even this was vastly inferior to the Krakatoa catastrophe, 

 and almost all the prominent scientific men of the day concur in connecting 

 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-crystals 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 



