THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL 



Vol. V. 



Washington, D. C, June, 1884. 



No. 6. 



Volcanic Dust. 



Much has been written about the 

 remarkably brilHant colors of the sky 

 at sinirise and sunset observed several 

 months ago, and speculations as to 

 their cause were, as usual when any- 

 thing remarkable occurs, numerous 

 and often quite as surprising as the 

 phenomena themselves. Strange to 

 say, the explanation that seemed to 

 meet with most general acceptance, 

 that of volcanic dust, was one which 

 very brief consideration would have 

 shown to be quite untenable, while 

 the most obvious and reasonable of 

 all. which certainly must have imme- 

 diately presented itself to the minds of 

 meteorologists as it did from the be- 

 ginning to ourselves, received but lit- 

 tle prominence in the public press. 

 The after-glows were probably caused 

 by aqueous vapor in some form in the 

 higher regions of the atmosphere ; 

 possibly by particles of dust of me- 

 teoric origin. 



The subject, however, has drawn 

 attention to the importance of micro- 

 scopic examination of atmospheric 

 dust, several specimens of which have 

 been recently sent to the National Mu- 

 seum for this purpose, from widely- 

 separated localities. Thus far nothing 

 remarkable has been observed in any 

 of them, but as the collections increase 

 it may be hoped that interesting re- 

 sults may be obtained. 



It is not unfrequently that dust is 

 collected many miles from land on 

 the sails of ships. Ehrenberg has 

 recorded several showers of dust, 

 containing infusorial remains, which 

 must have been carried many miles in 

 the air ; and other observers have 

 noticed the same phenomena. All 



dust so collected is by no means of 

 volcanic origin ; frequently it contains 

 infusorial remains, but in most in- 

 stances k resembles the fine dust 

 which may be taken up by the wind 

 almost anywhere, and no indication 

 of its place of origin can be found by 

 examination. For example, we have 

 recently examined the sediment from 

 some discolored snow which fell in 

 the vicinity of Rome, N. Y., last 

 February. The discoloration was 

 evidently caused by fine particles of 

 dust which had been taken up from 

 some unknown locality, and resem- 

 bled what would be found on any 

 dusty road in the country. 



Since the eruption of the volcano 

 Krakatau, specimens of dust have 

 been collected in various parts of 

 America and Europe which have 

 been regarded as cinders from the 

 volcano carried in suspension in the 

 atmosphere. M. Renard, in view of 

 the interest lately aroused in the sub- 

 ject, presented a verbal communica- 

 tion before the Belgium Microscopical 

 Society, upon the microscopical char- 

 acters of the volcanic ashes of the 

 eruption of Krakatau. We condense 

 from the Bullcti>i dcs Seances the 

 following obsei"vations of M. Renard : 



Although it is not difficult to de- 

 cide upon the eruptive nature of vol- 

 canic specimens of sufficiently large 

 size, one cannot affirm so positively 

 concerning volcanic particles in the 

 form of ashes. It may be said that 

 it is neither the presence of volcanic 

 minerals nor the structure of minute 

 vitreous particles which enables us to 

 distinguish the eruptive nature of dust 

 from the atmosphere. Minerals re- 

 duced to such infinitesimal dimensions 



