528 Royal Astronomical Society, 



have already been obtained, and the promise afforded of future im- 

 provements, the Council doubt not that the Society, and astronomers 

 in general, will ratify its decision. 



The President then, addressing the Foreign Secretary, continued as fol- 

 lows : — 

 Mr. Rothman, — In transmitting this medal to Professor Hansen, 

 assure him of the lively interest which this Society takes in the con- 

 tinuance of his important labours ; and convey to him our warmest 

 wishes for his health and happiness, that he maybe enabled to com- 

 plete those improvements in the most arduous departments of our 

 science which he has so auspiciously commenced, and thereby ac- 

 quire a still stronger title to the gratitude of astronomers, and to a 

 place among those who have most signally contributed to the deve- 

 lopment of the theory of Newton. 



The Meeting then proceeded to the Election of the' Council for the 

 ensuing Year, when the following Fellows were elected, viz. 



President : the Right Hon. Lord Wrottesley, M.A., F.R.S. — Vice- 

 Presidents : Francis Baily, Esq., F.R.S. ; Rev. George Fisher, M.A., 

 F.R.S. ; Sir John F. W. Herschel, Bart., K.H., M.A., F.R.S. ; Rev. 

 Richard Sheepshanks, M.A., F.R.S. — Treasure?- : George Bishop, 

 Esq.— Secretaries : Rev. Robert Main, M.A. ; Richard W. Roth- 

 man, Esq., M.A. — Foreign Secretary : Thomas Galloway, Esq., M.A., 

 F.R.S— Council: George Biddell Airy, Esq., M.A., F.R.S., Astro- 

 nomer Royal ; Rev. W. RutterDawes ; Augustus De Morgan, Esq. ; 

 Thomas Jones, Esq., F.R.S. ; John Lee, Esq., LL.D., F.R.S. ; Major- 

 General C. W. Pasley, R.E., F.R.S. ; Lieut. Henry Raper, R.N. ; 

 Edward Riddle, Esq. ; Lieut. William S. Stratford, R.N., F.R.S. ; 

 Charles B. Vignoles, Esq. 



April 8. — The following communications were read: — 



I. On the Aggregate Mass of the Binary Star 61 Cygni. By 

 S. M. Drach, Esq. 



The truth of universal gravitation having been confirmed by the 

 elliptic form of the orbits of binary stars, it follows that knowing 

 the absolute distances of the component members and their period 

 of revolution round each other, we are able to deduce their aggre- 

 gate mass compared with that of our sun and a planet, by exactly 

 the same process which acquaints us with the various masses of the 

 planets which are attended with satellites. 



The ratio of the sums of the masses of the component bodies in 

 two such systems being then that of the cubes of the mean distances 

 of the components, multiplied into that of the inverse squares of 

 their periods of revolution round each other, we may assume that 

 one system is composed of the earth and sun, and we have then 

 two cases to consider : 1st, when this binary star is of very small 

 mass compared with the sun, in which case the system would revolve 

 about the sun, the centre of gravity being near the sun's centre ; 

 and, 2ndly, when the star's mass is much superior to that of the 

 sun, in which case the orbital motion of the star would be only 



