122 Appendix. 



snow. On the third, the wind was quite high at Chicago, from 

 the southwest. At points south and west there seems to have 

 been quite a gale, with clear weather and very cold, with previous 

 falls of snow. The full reports were not obtained from Chicago, 

 and the force of the wind is not, therefore, known. 



Assuming that we -now have the main facts and circum- 

 stances which relate to the phenomenon, it remains to be ac- 

 counted for by some rational theory. What the true theory is, 

 it will perhaps be impossible to say ; but those which will natur- 

 ally present themselves, are first, Could the dust have its source 

 in some neighboring manufacturing establishment, and have 

 escaped from some high chimney or smoke stack ? 



A second theory might perhaps suggest a meteoric origin. 



A third would say that far enough southwest to find dry 

 prairie soil, neither frozen nor covered with snow, a powerful 

 tornado or whirlwind occurred, of sufficient magnitude to carry 

 this great quantity of dust high enough into the air to meet the 

 anti-trade wind, and crossing Lake Michigan, it was deposited 

 with the heavy snow storm which fell in that region. 



Again, could the dust in question be derived from Chicago ? 



Finally, the sediment may be of volcanic origin, borne by 

 the force of volcanic eruption to the upper current, and thus car- 

 ried to its place of deposit. These are the more likely theories 

 which are to be advanced, and the derivation of the substance 

 is probably due to one of these causes. 



Before going into any discussion of them, however, it will 

 be well to notice that this is by no means an isolated case. Phe- 

 nomena of an analogous nature are very numerous, and have been 

 the occasion of a good deal of investigation and inquiry. By stat- 

 ing some of the more important of these cases, and tracing a 

 similarity, if possible, between them and the present occurrence, 

 we may perhaps arrive at a more definite conclusion as to its true 

 cause. It would be quite an error to confound the phenomenon 

 which we are now considering, with any of these prodigies, a 

 great number of which are collected and noticed in Flammar- 

 ian's work on the atmosphere ; such as showers of sulphur, 



