Royal Astronomical Society. 221 



prising 170 nebulae and clusters, 580 double stars, 20 binary systems, 

 and 80 triple and multiple stars. The magnitude, colours, &c. of the 

 stars are carefully noted ; there are numerous comparisons with the 

 results (published and unpublished) of other observers ; and the 

 proper motion of the primary of each system is given with care. 

 This scientific information is accompanied with much antiquarian 

 research and literary history, and the work is likely to prove ex- 

 tremely attractive to the general reader. But the value of the work, 

 in reference to the Medal of this Society, is derived almost entirely 

 from its measures of double and multiple stars, and to these I shall 

 confine my further remarks. 



The subject of the labours for which this Medal is awarded is in- 

 teresting ; and the circumstances under which the Medal is awarded 

 are peculiar. It is incumbent on me to make a few remarks upon 

 the subject, and to explain the circumstances to which I allude ; but, 

 after the Report which has so long engaged your attention, it is ne- 

 cessary for me to be brief. 



The astronomy of double stars may be stated to have commenced 

 with Mr. W. Herschel's paper in the Philosophical Transactions, 

 1782. It is, therefore, essentially a modern science. But it is worth 

 while to remark that it was not then begun with the views which 

 have since become the principal motives for pursuing it. It was 

 begun with the intention of discovering whether the observations of 

 stars presumed to be at very different distances, but nearly in the 

 same position as seen from the earth, would exhibit any indication 

 of the earth's annual parallax. No such indication was discovered ; 

 but an unexpected and perhaps a more important result was in no 

 long time deduced from the observations. The relative places of the 

 components of a double star were found to change, and the change 

 had no respect to the position of the earth in its orbit, but went on 

 from year to year. In several instances the change altered its cha- 

 racter so completely, that it could be represented in no way but by 

 supposing that one star revolves round the other. And from that 

 time the observations have been pursued almost exclusively with the 

 view of tracing the orbits of binary stars. 



One step of great importance has been made. Methods have been 

 successfully introduced for the investigation of the elements of the 

 orbits of double stars, on the supposition that the law of gravitation 

 applies to them. And these methods have been applied to many 

 stars, and from the elements so computed ephemerides have been 

 prepared, by means of which the theoretical position of the double 

 stars, computed on the same law of gravitation, may be compared 

 with the position which shall be observed in the heavens. 



To complete this outline of the progress of double-star astronomy, 

 it appears only necessary to add, that it is believed that not more 

 than one or two stars have completed their revolutions since they 

 were first observed, and that there is no sufficient evidence that the 

 same orbit has been retraced in successive revolutions. 



Had I attempted, gentlemen, to enter more in detail into the hi- 

 story of this science, I should have done little more than weary you 



