452 



Moreover, 2ndly, about a quarter of an hour after the band was 

 first observed, being then on the roof of my house and having a 

 very uninterrupted view of the w^estern horizon, I noticed the for- 

 mation of a small streak of cloud about the same apparent altitude, 

 somewhat to the north of the pyramid of the zodiacal light, and 

 therefore nearer to the place of the sun below the horizon. The 

 direction of this streak was horizontal, not oblique, and its hue 

 black, not white. This cloud enlarged and became projected as a 

 dark space within the zodiacal light, and soon after others of a less 

 defined character formed elsewhere, all, however, without exception, 

 dark instead of luminous. 



Srdly. At the rising of the moon, about half-past eight, the 

 light of our band, already probably on the decrease, was almost 

 wholly effaced. On the other hand, by this time numerous lines 

 and cirrous streaks of light cloud which had been for some time in 

 progress of formation, and had been either wholly unseen before or 

 only noticed by their effacing the stars behind them, became illu- 

 minated, and appeared as white streaks and patches, such as are 

 usually observed in moonlight nights. 



4thly, and lastly. Although the night was very calm, yet on 

 watching narrowly the motions and changes of these real clouds 

 with respect to the stars, they were perceived to rise very slowly 

 from the west, i. e. in a direction nearly or quite contrary to that of 

 the declining band. 



From these united considerations, and from the extreme fixity of 

 the band among the stars, I consider it impossible to regard it as a 

 cloud illuminated by the sun through the medium of atmospheric 

 refraction. The latter reason, too, is equally conclusive against its 

 being classed with ordinary auroral bands and arcs, which, though 

 they keep their position well enough to be regarded as at rest by a 

 careless observer, yet, when compared with stars, are always per- 

 ceived to be drifting, as it were, in some certain direction, or other- 

 wise changing in figure and dimension. 



If we look to an origin for this phenomenon beyond our atmo- 

 sphere, we become involved in speculations, which, however inter- 

 esting, it is not the object of this communication to enter into. 

 On the other hand, its purpose will be answered if either it should 

 be the occasion of eliciting corresponding observations of the same, 

 or notices of similar phenomena already observed, or should lead 

 to increased watchfulness on the part of meteorologists to avail 

 themselves of occasions (which perhaps occur oftener than we are 

 aware) of noting anything analogous in future. 



I have the honour to remain, 



My dear Sir, 

 Your very faithful and obedient Servant, 



J. F. W. Herschel. 



Saturday, March 18, 1843. 

 P.S. — There having been no post today, and the above not having 

 been finished in time for despatch last night, an opportunity is af- 



