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large-sized cloud it must liave come from a great distance and 

 would have appeared as a nebulous patcb, whicli as it 

 approached could hardly fail to be noticed by some of the 

 numerous astronomical observers. But of such a phenomenon 

 we have heard nothing. We know that cometary tails are 

 Tery attenuated, and on the occasion not long ago when we 

 expected to pass through the tail of a comet there were no 

 extraordinary sun glows recorded. The date of this transit, as 

 predicted by Mr. Hind, was June 30th, 1861, and there is very 

 little doubt that the earth did pass through this tail. If the 

 -earth passed through fairly it must by reason of its atmosphere 

 have cleared a pencil 8,000 miles in diameter at the very least 

 and half a million miles long, of all the fine matter in that 

 path of the earth, and yet have done this without producing 

 any niptrked meteorological changes. If the tail were composed 

 of vaDOur frozen or otherwise it must have been remarkably 

 attenuated, and if dust or meteoric matter it must have been 

 ■exceedingly fine, as no display of incandescence took place. 

 The only thing noticed was a number of long faint streamers 

 pointing to the nucleus of the comet and widening out. It is 

 strongly probable from this that if a cloud of meteoric dust or 

 if a cloud of aqueous vapour sufficiently extensive or dense to 

 have supplied the atmosphere for these displays, had approached 

 the earth, such clouds could not have escaped observation 

 during both their approach and departure. 



The polariscopic examination affords very strong evidence of 

 watery vapour as the cause of the displays. From an extended 

 scrutiny during the whole period the following facts are 

 adduced by the writer • — The skylight is over the greatest 

 portion polarised in planes passing through the sun. There is 

 a neutral place in the sky. It varies in position, beiug farther 

 from the sun towards evening and early in the morning. It is 

 not always a point, sometimes it is an elliptic area difiicult to 

 define within nice limits. The term dark side is here taken to 

 represent the east side in the evening and west in the morning. 

 •On the dark side of the sky the polarization is about at right 

 angles to that of the sun side. This, however, is not constant. 

 AV"hen there is a reddisli tint on the dark side the polarization is at 

 a tangent to the principal boundar}^ of the tinted surface. This 

 area generally has an altitude of about 30^, varying in shape 

 and rarely 2)assing the neutral point position. AVhen the 

 red tint is not apparent the space below the neutral point is 

 brightest with the nicol in cross position. The form of 

 this space in dry air and clear evenings, when tinted, 

 Tesembles two spear-like columns thickest at the base and 

 inclined to each other, crossing at the top. On evenings when 

 there is to be a glow the red tint appears first on this dark side. 



