482 Royal Astronomical Society. 



be sent to England ; or should you wish any further information 

 respecting it, you will do him a favour by writing to him at Malta. 

 I shall not be here above a month longer, as I go on to Egypt with 

 my family in January ; but M. Wettinger being fixed to this spot, 

 will always be available. — I remain, &c. 



" Basil Hall." 



II. A Letter from Professor Henderson to the Secretary, dated 

 Edinburgh, January 31, 1842, on the Determination of the Parallax 

 of a Centauri, by recent Observations made by Mr. Maclear at the 

 Cape of Good Hope*. 



" My dear Sir, — Within these few days I have received from 

 Mr. Maclear a series of observations of a 1 and a 2 Centauri, made 

 with a view to ascertain the parallax ; and I find that they confirm 

 the existence of a parallax amounting to about one second. The 

 observations are of the double altitudes of the stars made with the 

 mural circles, and they extend from April 16, 1839, to August 12, 

 1840. Twenty-six observations of the double altitude of each star 

 were made with the old circle between April 16 and June 16, 1839; 

 and 108 observations of the double altitude of a 1 , and 112 of a 9 , 

 were made with the new circle between August 4, 1839, and August 

 12, 1840. In each observation the star was observed both by direct 

 vision and by reflexion at the same transit. The results which I 

 have obtained are as follow : — 



" From the 272 observations made with both circles, 



Parallax = 6-91. Weight 147*93 observations. 

 Coefficient of Aberration = 20-55. ... 142*47 ... 



" From the 220 observations made with the new circle, 



Parallax = 6*92. Weight 138-81 observations. 

 Coefficient of Aberration = 20-53. ... 12797 



" The observations made with the old circle extend over too short 

 a period to warrant any results beng deduced from them alone for 

 parallax and aberration which could be relied upon. 



" On computing the observations of each star separately, I find 

 for a 1 , — 



" From the 134 observations made with both circles, 



Parallax = 0-86. Weight 70*37 observations. 

 Coefficient of Aberration =20-61. ... 70*02 



" From the 108 observations made with the new circle, 



Parallax = 0*91. Weight 65*83 observations. 

 Coefficient of Aberration = 20-54. ... 63*71 



" And for a-, — 



* Former observations on this subject are noticed in Phil. Mag. S. 3. 

 vol. xvi. p. 148 ; vol. xviii. p. 599. — Edit. 



