208 Scientific TnteUigence — Meteorology. 



nectioii with their Geological Structure and Composition ; with 

 Specimens, and a Map of the Distribution of the Plants. In this 

 Essay, the range of elevation and the northern and southern limits 

 of the different species should be attended to, and any facts tending 

 to illustrate the geographical distribution of plants carefully recorded. 

 It would also add greatly to the interest of the communication, if it 

 were accompanied with a coloured Geognostical Map of the moun- 

 tainous districts examined. — Time, February 1 844. 



SCIENTIFIC INTELLIGENCE. 



METEOROLOGY. 



1. Bahinet upon the Blue Sun. — Upon the occasion of Mr 

 Forbes's communication concerning the sun seen red across 

 steam, allow me to inform the Academy, that, in studying the 

 phenomena of meteorological optics, I have not neglected those 

 colours which the sun and moon occasionally assume, of an ex- 

 ceedingly dull tint, and without any surrounding rings. The 

 phenomenon of a red sun may be attributed to a defect in the 

 transparency of the atmosphere arising from vapovirs, or to 

 any other cause ; for the fundamental interval of interferences 

 being much greater for the red than for the blue and violet, 

 these latter are first extinguished, and the obstacles to their 

 transmission are comparatively much greater than to the trans- 

 mission of the red, as is the case with the reflection from a glass 

 that has been merely smoothed, which always begins with the 

 red. Upon this I may remark, that it is very doubtful if the red- 

 dish-brown tinge of smoked rock-crystal is owing to a true colour 

 and not to the exclusion of the lower colours of the spectrum 

 induced by the imperfect transparency of the foreign matter. 

 Another phenomenon, which is much more rare and curious 

 than the red sun, is the blue sun, Avhen this luminary is seen 

 of a fine blue tint, though somewhat mixed with white. Our 

 scientific repositories contain some instances of this, and I have 

 myself seen two. It is evident, that the yellow hue, vv^hich is 

 much less remarkable on account of its analogy with the white, 

 must also frequently occur, whilst the violet, owing to the 

 difficixlty with which it traverses imperfectly diaphanous me- 



