28 



Rev. B. Powell's Observations 



minated on groups of milky white oprt(]ue felspar, most of the 

 crystals of which are covered with a thin dark iron black coat- 

 ing, and n)ica hi large laminse. These crystals offer only two 

 varieties; one of which is represented by fig, 2, and the other 

 differs from it by the absence of the planes bi *'. 



They generally present both 

 summits. The planes m and Z*' are 

 very brilliant, the planes b^ and bl 

 dull, and the planes g ' slightly un- 

 dulated and of a highly vitreous 

 lustre. Their colour varies from 

 grayish white to a deep brown. 

 Some are transparent ; others only 

 transluscent or opaque. Some of the 

 crystals are as large as a wallnut, ge- 

 nerally much smaller, but very well 

 defined. 



IX. Observatiojis on the Solar Eclipse, November 29th) 1826. 

 Bj/ the Rev. Baden Powell, M.A. F.R.S. 



To the Editors of the Philosophical Magazine and Annals of' 

 Philosophy. 



'T'HE curious observations of Mr. Wiseman during the 

 *■ solar eclipse of September 1820, recorded in the Memoirs 

 of the Astronomical Society (Part I. p. 140.) tend to show 

 that during the eclipse there was a deficiency of the red rays 

 of the sun and the heating power accompanying them. This 

 conclusion is considered to be corroborated by the further 

 observation of a diminution in the space occupied by the red 

 rays in the prismatic spectrum formed at the same time. The 

 facts are stated to have been anticipated by Mr. Wiseman ; but 

 the principle on which he anticipated them is not mentioned. 



As there is nothing said in the paper alluded to, which can 

 lead us to determine how far the effects may depend upon the 

 magnitude of the eclipse, it will be doubtless a point of in- 

 terest, not only on the occurrence of an eclipse of equal mag- 

 nitude to verity the facts ; but also in other cases to ascertain 

 whether, or in what degree, similar effects are produced. 



With this object in view, I made a few observations during 

 the eclipse of November 29th. The weather was favourable 

 only for one short interval in the early part of the eclipse, 



* Since writing the above, I have observed another variety whicli be- 

 sides the modiiications of fig. 2. presents the planes, which Haiiy has desig- 

 nated by .r. 



and 



