150 Atmospheric Origin of the Aur07X(, ^*c. 



light, and the crystals be, under some circumstances, magnetic ; 

 and in relation to the 9th remark, has inquired, ' May not this 

 expression be used as something more than a figure of speech ? 

 What is so likely to produce this structure, so regular, and yet so 

 complicated, as the polarity of component crystals, whether this 

 polarity is or is not magnetic ? May not the ponderable material 

 of the colonnade of an aurora borealis consist of similar groups of 

 crystals, formed either from the vapor of water, or from some 

 lighter, less conden&ible and more magnetizable vapor in the 

 upper regions, which crystallizes at the same time, and under 

 similar meteorological influences with the former ?' Has not 

 the crystalline character of the higher clouds, if it exists, been 

 generally overlooked by meteorologists ; and when they have 

 represented all clouds as being masses of condensed vapor, and 

 snow as resulting from its subsequent congelation, have they not 

 overlooked the universally crystalline character of snow, forgot- 

 ten the small height which is necessary for crystallization, and 

 suffered their imaginations to be influenced by their own tempe- 

 rate climes and moderate elevations ? 



In advancing a step farther in the attempt at an explanation of 

 the intimate nature of the phenomenon, and especially as con- 

 nected with aqueous crystals, the author has ventured with difli- 

 dence upon a topic still more recondite and obscure, but has found 

 some support in analogies drawn from the electrical light seen 

 during the crystallization of water, from the induction of crystals, 

 and the magnetism developed by changes of temperature in many 

 crystalline substances ordinarily unmagnetic. That iron^ proba- 

 bly from its magnetic properties, has a peculiar relation to the 

 crystals of hoar frost, he has been led to suspect, from their ten- 

 dency to -assume a position at right angles to the edges of a mag- 

 net and of a tinned vessel, at temperatures between zero and — 12°, 



' In experiments with the solar microscope, I have been struck 

 with the analogy between the polarity of crystals and that of 

 magnets, a polarity evinced by the rotation of the smaller groups, 

 in their approach to the larger and more complicated ones. The 

 extent of rotation produced in one group by another never ex- 

 ceeded 180°. I have also detected a still more interesting anal- 

 ogy in the influence which a large group exerts upon the forma- 

 tion of smaller ones at a considerable distance. There was a real 

 induction. This was evident from the fact that a large nucleus 



