382 Transactions. — Miscellaneous. 



Let us, therefore, in the last place examine the objections that either are 

 or can be, in my humble opinion, urged against the dust theory. 



1. The amount of dust that would be requisite to form even a thin belt 

 over so large an area of the earth's surface as is comprised, say, between 

 the 52nd parallel of north latitude (that of London), and the 44th parallel 

 of south latitude (that of Dunedin), — that is to say, roughly speaking, 

 about 150 millions of square miles, — would be so enormous that it is difficult 

 to believe that it could all have been thrown up by Krakatoa. We must 

 allow this to be a forcible objection ; but reflect at the same time on what 

 has been said as to the gigantic scale "of the operations at Krakatoa, and 

 furthermore consider two points : — (1) That the dusty cover need not have 

 been, as far as I know, very thick, and the third dimension, the thickness of 

 the cover, would materially affect the total amount of its solid contents ; (2) 

 That the dust was probably not distributed equally thickly or densely over 

 the whole of the vast area ; indeed one can well understand that it hung 

 suspended only in particles, for there were undoubtedly periods of intermis- 

 sion in the displays, and these intermissions may have been occasioned by 

 the temporary absence of the causal medium as well as by other counter- 

 acting atmospheric conditions. What do we really know for certain about 

 either the exact amount of dust ejected from Krakatoa or that requisite for 

 producing the phenomena ? Very little I imagine. 



2. Tt is said, even if dust had been shot up to an enormous height by 

 the Krakatoa eruption, from its inherent weight it would soon have settled 

 down on the earth again (Professor Eees). Undoubtedly the heavier particles 

 would have done so, and actually did so ; but in proportion to the minute- 

 ness of the particles in all probability would be the distance and time they 

 would travel. The heavier dust fell at Krakatoa, but we have read of thick 

 dust falling on a vessel at sea many hundred miles away. One writer sug- 

 gests that the air may possess some viscosity which would check the ten- 

 dency of the dust to settle. Moreover, Professors Preece and Crooke say 

 that minute particles ejected into the upper air would be negatively electri- 

 fied, and therefore repelled by the earth and by one another (which, by the 

 way, would account perhaps in part for their rapid diffusion) and so would 

 probably remain at a high level for a long time. Besides the lower strata 

 of the atmosphere itself might be denser than the foreign matter of the 

 upper strata — even though not composed of exceptional gases ejected from 

 Krakatoa. Eollo-Eussel points out, too, the vesicular nature of pumice, 

 each particle really consisting of a bubble of glass — which, when shot high 

 and removed from the action of vapour and weather, would be easily carried 

 to the most distant parts of the globe (" Hard. Sci. Gos."). Very fine dust 



