496 



Note by Dr. Benza. 



[Oct. 



went prevented this from being effected. M. Arago, therefore, adopt- 

 ed another method. On the 23d October, having applied an apparatus 

 adapted for observation, he saw two images, which presented comple- 

 mentary tints, one red, the other green. By making a half revolution 

 of the telescope upon itself, the red image became green, and vice 

 versa. " Thus the light of the star, was not completely, at least, com- 

 posed of rays endued with the properties of direct light, peculiar or 

 assimilated; it contained some light reflected specularly or polarized, 

 that is to say, definitely, some light proceeding from the sun." 



Note. 



The author of the Memoir on the Geology of the Neelgherry and 

 Koonclah Mountains, having written the article while on the Hills, could 

 not consult the vol. ( 13th) of the Edinburgh Philosophical Journal, 

 in which Dr. Daubeny's sketch of the geology of Sicily was pub- 

 lished ; and therefore was unable to transcribe the Professor's passage 

 regarding the cavities of large dimensions in the limestone of Monte 

 Pellegrino, near Palermo. Having since returned to Madras, the fol- 

 lowing paragraphs, illustrative of the subject in question are added 

 here : " Before I quit the subject of the Palermo limestone, I must 

 not omit a circumstance relative to the rock of Monte Pellegrino, 

 near that city, which seems to deserve notice. Notwithstanding the 

 uniform compactness, of this stone, wherever it has been recently 

 quarried, we find it in these parts, which have been exposed to the 

 weather, honey-combed in an extraordinary degree, by holes of con- 

 siderable size, which penetrate several inches below the surface, but 

 indicate from the gradual decrease of their dimensions, that the cavi- 

 ties were formed by the action of the weather, sinking gradually into 

 the substance of the stone. 



" These cavities in their size and appearances, reminded me of those, 

 which occur near the surface of a hard silicious limestone belonging 

 to the oolite formation in Gloucestershire, which has obtained the 

 local name of the ( Dagham limestone.' " 



The reader will easily see from the above quotation, that what Dr. 

 Daubeny says about the cavities having been formed by the action 

 of the weather, sinking gradually into the substance of the stone, is 

 analogous to the lodging of a drop of water spoken of by Dr. Mac- 

 culloch, and that it is similarly inefficient as a cause of these large 

 corrosions in the limestone 3 as that of Dr, Maccuiloch for those in the 

 granite.— P. M. B. 



