602 THE POPULAR SCIENCE MONTHLY. 



bright emerald, as pure and brilliant as ever gem that glistened ; again 

 we lose it, and again an opening shows it to us in its own golden light ; 

 and then once more it is the bright green ; and now it rises higher, 

 clears the ridge, and is once more the golden orb." The Rev. G. H. 

 Hopkins, of Cornwall, England, has observed that in a clear sky, as 

 the disk of the sun sinks down beneath the horizontal line of the 

 ocean, the parting ray is of a deep emerald green. The effect is not 

 produced if there are clouds around the sun. Dr. F. A. Forel, of 

 Morges, Switzerland, mentions as a fact confirmatory of the opinion 

 that meteorological factors alone can not furnish a sufficient explana- 

 tion of the phenomenon, that in Switzerland the glow, after having 

 decreased subsequently to the 3d of December, attained a second 

 maximum on the 24th and 25th of the month, when the atmospheric 

 conditions were quite different from those which prevailed in the coun- 

 try at the time of the first maximum. 



The hypothesis that the spectacle was caused by the presence in 

 the atmosphere of a cloud of " cosmic dust," which the earth has en- 

 countered in its travels, has been advanced by several observers, and 

 is supported by Mr. Proctor. Mr. Nordenskiold and other men emi- 

 nent in science have taught us to believe that a meteoric dust falling 

 upon the earth from space plays a much more important part in ter- 

 restrial economy than we have been accustomed to suppose ; and they 

 have collected, in uninhabited countries and far away from any vol- 

 cano, quantities of dust little rounded particles of metallic com- 

 pounds unlike anything the earth is known to produce, and strik- 

 ingly like what meteors of that size would be. Investigating whether 

 an unusual quantity of such dust is now falling upon us, Mr. W. 

 Mattieu Williams has found it in carefully selected snow from his 

 garden. M. Emile Yung, of Geneva, has also found an extraordinary 

 quantity of a similar dust in fresh snow that fell in the latter part of 

 November and early in December on the steeple of the cathedral of 

 Saint-Pierre, at " les Treize-Arbres," Mont Saleve. 



Numerous suggestions have been made that the phenomena are the 

 result of the diffusion through the whole atmosphere of the entire 

 earth of ashes and cinders from the eruption of the volcano of Kraka- 

 toa, in the Straits of Sunda, which took place on the 26th of August 

 last. This theory has the support of Professor Lockyer and other emi- 

 nent men of science, and there is much to be said in favor of it. The 

 principal objections to it are summarized in a remark by Mr. Proctor, 

 "that we should have to explain two incongruous circumstances : first, 

 how the exceedingly fine matter ejected from Krakatoa could have so 

 quickly reached the enormous height at which the matter producing 

 the after-glow certainly was ; and, secondly, how, having been able to 

 traverse still air so readily one way, that matter failed to return as 

 readily earthward under the attraction of gravity." It will not do to 

 limit our ideas of the effect that may have followed the eruption of 



