Meeson. — On the recent Sun-glows, 869 



it was gradually drawing towards the pole, and that it was connected 

 with the Sunda eruption. But that the exceptional matter in the upper 

 air is vapourous at all seems to me very doubtful. I would remark here 

 parenthetically that it is very easy for us to be wise when a great many 

 facts and opinions have been given and collected ; but very difficult when 

 the phenomena are quite new and few accurate observations have been 

 made, and we have had no opportunity of comparing notes with other 

 observers. To say this much is due to those who, from their position, are 

 expected at all times and at a moment's notice to give a correct opinion as 

 to the cause of whatever baffles ordinary comprehension in natural pheno- 

 mena. That they should occasionally make a mistake is to be expected, 

 but that they have done so as far as this aqueous theory is concerned, I con- 

 ceive, as yet, is certainly " not proven." That they have, in some cases, 

 changed their opinion, shows the difficulty and uncertainty with which the 

 whole subject is surrounded. 



However, there is another test of the "aqueous vapour" theory — the 

 spectroscope. When the glow is examined by means of this tell-tale instru- 

 ment, if there were aqueous vapour in any quantity in the upper air, 

 you would have the solar spectrum with its Fraunhofer lines and 

 certain black bands — wet weather or rain bands as they are called 

 — intervening, even as when a ray of light is seen through straum 

 (M. Jansen). Now, as a matter of fact, during the period of the sun- 

 glows, whenever the spectroscope was employed, it was found that the 

 rain bands instead of being at a maximum were at a minimum. On the 

 other hand, the dry-air band was well defined — in fact, to use the words of 

 Lockyer, it was at a tremendous maximum. Notwithstanding some evi- 

 dence to the contrary furnished by Mr. Michie Smith, of Madras, and Dr. 

 Assman, of Maddeburg, this seems at first sight pretty conclusive. But it 

 is not so, for there arises this question, Would the spectroscopic effect be 

 altered according to the condition of aqueous vapour in the upper air ? If the 

 vapour were turned by the intense cold of the upper currents into icy 

 particles, Would the rain band then appear ? I do not think it would, and 

 we shall see subsequently direct testimony that it would not. So that, after 

 all, the aqueous vapour theory does not completely break down — it only 

 becomes modified. We have ice crystals instead of watery vapour. I read 

 that green and blue suns are frequently seen in polar regions ; and icy par- 

 ticles in the air refracting the sun's light into its prismatic components are 

 very favourable for the display of sunset colours (" Hard. Sci. Goss.") The 

 question is, what other independent proof have we that the upper air has 

 been full of ice crystals ? The general view of the world's weather 

 recently does not seem to provide any evidence in this direction. Some 

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