178 



The following Gentlemen were duly elected Ordinary 

 Fellows : — 



Henky Davidson, Esq. 

 Rev. J. Hannah, M.A. 



The following Donation to the Library was announced : — 



First Report on the Coals suited to the Steam Navy. By Sir Henry 

 De la Beche and Dr Lyon Playfair. Fol. — By Sir Henri/ 

 De la Beche. 



Monday, 3rf April 1848. 



Sir THOMAS MAKDOUGALL BRISBANE, Bart., 

 President, in the Chair. 



The following Communications were read : — 



1. Notice of the Orbit of the Binary Star a Centauri, as re- 

 cently determined by Captain W. S. Jacob, Bombay 

 Engineers. By Professor C. P. Smyth. 



The object of this paper is to point out the extremely important 

 and interesting characteristics of the orbit of the two stars of a Cen- 

 tauri round their centre of gravity, with the object of procuring as 

 many observations as possible from southern observers during the 

 periastral passage in 1851-5. 



Professor Henderson and Sir J. Herschel, the only two observers 

 who had specially applied themselves to the subject previously to 

 Captain Jacob, were not able to make any thing of it, with such 

 materials as had been accumulated up to their time. They merely 

 ventured to predict, that a very close affinity of the two stars 

 might be expected about the year 1867 ; and both seemed to consider 

 that the period of revolution was something very great, — that the 

 star was increasing in distance at the time that it was observed by 

 Lacaille in 1751, and byMaskelyne in 1761 ; and that it had occupied 

 the intervening time in reaching its maximum distance, without any 

 sensible change of angle of position. 



Sir J. Herschel, in concluding his review of the subject, said, " that 

 no subject more worthy of continued and diligent attention could 

 possibly be urged on the attention of southern astronomers ;" and this 

 has since been most eminently borne out by Captain Jacob's obser- 



