Royal Astronomical Society. 521 



pectation, and that a distinguished career may yet await one of the 

 earliest and the most indefatigable friends of the Society. 



In the Address of the President at the last Anniversary of the 

 Society, honourable mention was made of Mr. Henderson's investi- 

 gations relative to the presumed parallax of a Centauri. These in- 

 vestigations have been continued to the present time ; and from some 

 observations recently received by him from Mr.Maclear, at the Cape 

 of Good Hope, he is confirmed in his opinion relative to this subject, 

 and considers the parallax to be about 1". The Council trust that 

 they shall soon receive from Mr. Henderson a detailed memoir on 

 this important subject, which will then be read at the ordinary meet- 

 ing of the Society. 



The Council regret that they have to announce the retirement of 

 Lieut. Raper from the office of Secretary to this Society ; an office 

 which he has filled with the greatest zeal and attention, and which 

 calls from this meeting the expression of their best thanks. Nothing 

 but the love of science and the talents which he possesses could 

 have induced him to take so active and important a duty, often- 

 times at a sacrifice of private ease and convenience : but this remem- 

 brance is at once the source of our approbation and the cause of our 

 regret. 



The Council trust that the award of the medal to Prof. Hansen will 

 meet the approbation of the Society. The labours of M. Hansen 

 are well known to those astronomers and mathematicians who have 

 attended to, and cultivated, that branch of inquiry which more espe- 

 cially relates to those abstruse and intricate points of investigation 

 that require the greatest exercise of mental exertion. The grounds 

 on which this award has been made will be more fully explained in 

 the Address of the President at the close of this Report. 



The President {the Right Honourable Lord Wrottesley) then ad- 

 dressed the Meeting on the subject of the award of the Medal, as fol- 

 lows : — 



Gentlemen, — Since the great discovery of the law of gravitation, 

 the means by which the astronomy of the solar system has been ad- 

 vanced to its present state of perfection are of two distinct kinds. 

 The first consists in the collection of facts from observation, — or, it 

 may be said, in the application of that complicated and refined sy- 

 stem of operations whereby the practical astronomer is enabled not 

 only to assign the exact positions which the several bodies belonging 

 to the system occupy at the moment of observation, but also to de- 

 termine the paths they describe in space, and the laws by which 

 their motions are governed. The second is that which is employed 

 by the geometer. Setting out from the law of gravitation as esta- 

 blished by Newton, and borrowing only from observation the ele- 

 ments which are necessary for the institution of his calculus, his ob- 

 ject is to deduce from theory alone the whole of the phenomena of 

 the system, even to their minutest details, and, by a comparison of 

 his results with observation, to determine the masses of the different 

 bodies, the influences which they exercise on the motions of each 



