18 Scientific Proceedings, Royal Dublin Society. 



the greatest interest and importance from the points of view of 

 meteorology and geology in general. I allude to the quantity of 

 gaseous vapour emitted during the eruption. This must have a 

 direct relation to the quantity of matter emitted (whatever its 

 form), and also to the height and distance to which the matter 

 may be ejected or carried. Now, I hold that such vast quantities 

 of gases as must have Tbeen liberated on this occasion cannot be 

 passed over, or taken as having no action on our atmosphere. 

 Whatever the addition made, temperature and air currents are 

 influenced by it, either locally, or over great extents of the earth's 

 surface ; and if it were possible to take account of the height 

 attained by the gases, their temperature at liberation, and the 

 point of the globe whence proceeding, some judgment might be 

 attempted of their action. In the present state of meteorology 

 we know nothing of these quantities, but it is justifiable to assume 

 that the upper currents of the air may be thus profoundly influ- 

 enced, and that in certain cases cyclones may thus be generated. 

 The present very fine dry weather we are enjoying here, with the 

 high and steady barometer, may be a result of the great eruption, 

 and it will be worth while to note if any abnormal conditions of 

 atmosphere be found to prevail during the coming months." 



It was not until October 11th that an article appeared, noticing 

 "a green sun in India;" therefore, quite subsequent to my letter. 

 During the following months the wonderful " glows " which illu- 

 mined the heavens, more particularly after sunset, interested men 

 of science of every country, and they have been very generally 

 attributed to the presence of vast quantities of dust in the upper 

 regions of the atmosphere — this dust being generelly presumed to 

 have resulted from the Krakatoa eruption. I may therefore, in 

 some degree, claim to have anticipated the appearance of these sky 

 glows, in so far as it is accepted that they are due to emissions from 

 Krakatoa. I now propose to examine more extendedly the con- 

 siderations upon which I based this anticipation. 



It may not be out of place to remark, that in the study of 

 natural phenomena we are easily led to attribute a relatively 

 greater importance to agents which impress our senses than to 

 those more occult in their action, and more particularly which do 

 not leave distinct evidence of their influence. Thus, it is only 

 quite recently that the role of dust in the formation of rain has 



