Mr Coldstream on the Rarer- Atmospherical Phenomena, 6?c. 85 



Art. XVII. — Account of some of the Rarer Atmospherical 

 Phenomena observed at Leith in 1825. By Mr John 

 Coldstream. In a Letter to the Editor. 



My Dear Sir, 

 In compliance with your request, I now send you a short ac- 

 count of the principal atmospherical phenomena observed here 

 during 1825. You are already in possession of a most accu- 

 rate history of the progression of temperature during the year 

 at this place, in the results of the Leith Fort hourly register ; 

 and any observations which I could communicate on the pres- 

 sure or humidity would probably be uninteresting ; I shall 

 therefore confine myself to descriptions of the rarer meteors 

 seen within our horizon in the course of the twelvemonth. 



On the 7th of February two colourless rainbows were ob- 

 served ; one at 9 A. m. and the other about noon. Much rain 

 had fallen during the preceding night, and the morning had 

 been cloudy ; but at the time of their appearance there were 

 no clouds visible, except towards the western horizon. In the 

 zenith the colour of the sky did not equal the 10th degree of 

 Saussure's cyanometer. The primaries only were seen ; they 

 were vivid and distinct throughout their whole extent, and had 

 the ordinary breadth of the common rainbow. While I was 

 observing the one which appeared at noon, I saw its northern 

 limb fall upon a portion of a nimbus in motion, and immedi- 

 ately assume the proper colours ; but whenever the cloud had 

 passed, the bow regained its colourless state. This phenome- 

 non is probably rare. I am not aware of its having been ob- 

 served by any of the older meteorologists ; but in Mr How- 

 ard's Climate of London, and in Mr Forster's Researches, 

 mention is made of similar appearances. Mr Howard says, 

 " About 10 a. m., 23d January 1808, a faint, but nearly per- 

 fect rainbow appeared under unusual circumstances. At the 

 time a few light clouds had begun to show themselves in dif- 

 ferent quarters, but none over the place of the bow, nor was 

 the falling mist that afforded it of sufficient density to obscure 

 the sky ; the colours were not visible, so that the rainbow had 

 the appearance of being white.* * 



* Dr Thomas Young, in his paper On the Measurement qf Minute 



