Intelligence and Miscellaneous Articles. SI 7 



and the reflected observations of declination. On resolving the 

 equations by the method of least squares, and assuming the coeffi- 

 cient of aberration to be 20 '06, Mr. Henderson finds the follovi^ing 

 results : 



Parallax of a' Centauri = 



-f 0"92 ; probable error 0''-35 ; from observations of right ascension. 



+ 1 •42 ; probable error '\^ ; from direct observations of declination. 



+ 1 '90; probable error •47; from reflected observations of declination. 

 And = + l"-38, with a probalile error of 0"-16, by taking a mean of the three 

 determinations according to their weight. 



Parallax of a- Centmn-i = 

 +0"^48 ; probable error 0"-34 ; from observations of right ascension. 

 -j-1 •OS ; probable error •IS ; fiom direct observations of declination, 

 -f 1 -21 ; piobable error ^64 ; from reflected observations of dechnation. 

 And = + 0"-94, with a probable error of 0"-ie, by taking the mean according 

 to their weights. 



If we suppose that the two stars are at the same distance, then 

 the parallax = + 1"-16, with a problem error of 0"-ll. It there- 

 fore appears probable, that these stars have a sensible parallax of 

 about one second of space. 



XLIX. Intelligence and Miscellaneous Articles. 



POSTSCRIPT TO THE COMMUNICATION OF PROF. SEDGWICK AND 



MR. MURCHISON IN THE PRESENT NUMBER AT P. 24.1. 

 V17E alluded to the possibility of the Devonian or Old Red Sy- 

 ' » stem being much developed in Ireland, and under mineral 

 characters analogous to those of Devon. In support of this view, we 

 may add, that since this paper was printed, Mr. Charles W. Hamil- 

 ton has called our attention to a paper read by him before the Geo- 

 logical Society of Dublin, in 1837, in which he described the rock 

 hitherto called grauwacke slate, which occupies a great extent in 

 the county of Cork, as lying conformably upon the old red sandstone 

 and conglomerate of the Gaulty Mountains and the Reeks in Kerry, 

 and supporting the carboniferous limestone into which it gradually 

 passes. 



Tliis red conglomerate rests unconformably upon a great thickness 

 of older slates and conglomerates, which Mr. Hamilton has described 

 as exactly similar to those which are exposed in a section made from 

 Mr. Pennant's quarries in Caernarvonshire to Ogwen. In a paper 

 read before the Geological Society of Dublin last month, Mr. Hamil- 

 ton has also stated his belief, that slates occupying a large space 

 between the Mourne and Dublin Mountains, are equivalent to those 

 in the immediate neighbourhood of Cork, and may therefore be re- 

 ferred to the old red sandstone. 



MR. CROSLEY S PNEUMATIC TELEGRAPH. 



In inserting the account of Mr. Crosley's pneumatic telegraph in 

 our last number, we had not space for some of the details, which we 

 therefore now give in continuation. 



In establishments where the telegraphic communications do not 

 require the constant attendance of a person to observe them, and 



