54 Astronomical Society. 



feet diameter, and is furnished with a position and parallel-thread 

 micrometer, possessing a variety of magnifying powers, from 55 to 

 625. The instrument was fitted up with a special view to the exami- 

 nation of the positions and distances of the multiple stars. Each part 

 of the micrometer .screw-heads is equal to 0",5559219." 



Mean result. Pos. of AB = 59° 13' n/(16 obs.) Dist. = 1",095 (7 obs.) 

 Pos. of AC = 60 17 sf{ 5 obs.) Dist. = 5 ,592 (5 obs.) 



After giving the observations, Mr. Dawes proceeds thus : — 



" Now, if we compare these results with the measurements of Sir 

 W. Herschel in 1781, and of Sir James South in 1825, a very extra- 

 ordinary variation appears. In 1781-90, Sir W. Herschel's measure 

 of the position of AB was 86° 32' nf. In 1825-27, a mean of 43 

 measures (the means of the six different sets on as many nights, 

 agreeing admirably together) gave as the position 32° 10'??/, offering 

 a difference of 54° 22' from the position in 1781, Now, however, 

 the angle lies as nearly as possible midway between the two, being 

 27° 19' less than that of 1781, and 27° 3' greater than that of 1825; 

 while the distance, as measured by me, is only 0",009 greater than 

 the result of 15 observations by Sir J. South, It would therefore, 

 appear as if the motion had been performed in a direct sense (or nfsp) 

 for perhaps thirty or forty years ; and that the star B had then come 

 to a stand, (or appeared to do so), faced about, and is now proceed- 

 ing in the opposite direction, which is the same pursued by the star 

 C But this is an extravagant idea ; and unless there exist obser- 

 vations in the intervening period to invalidate the supposition, I think 

 we may arrive at a solution of the difficulty in a more simple manner; 

 namely, that in the fbrty-nine years elapsed since Sir W. Herschel's 

 measurement, the star B has performed almost an entire revolution, in 

 a retrograde sense, or np sf, only about 27° or 28° being wanting to 

 complete it. 



" Mr. Herschel, in his notes appended to Sir J. South's valuable 

 paper, forming the first part of the Philosophical Transactions for 

 1826, has mentioned an observation of this star by his father in 1802, 

 • at which lime,' it is said, ' no measures could be procured.' Now, 

 supposing this to be the only observation recorded during the inter- 

 val, it may be asked. Would not Sir W. Herschel have been struck 

 with any remarkable alteration in the relative positions of A and B, 

 even supposing the circun^stances were not such as to admit of mea- 

 surements ? To this it may be replied, that it is highly probable the 

 star B would, about the year 1802, have arrived at that point of its 

 orbit in which it would be nearly opposite to its place in 17Slj and 

 the stars diftering but little in size, it might not be noticed, especially 

 in unfavourable circumstances, which preceded ; and, consequently, it 

 might easily be imagined to have sustained but little, if any, alteration. 



" The position of B now observed is the more remarkable, because, 

 had it pursued the course formerly assigned, its angle relative to A 

 would now be about 24° or 25° nf. That an error of 35°, or any 

 thing like it, should be committed in my measurements, appears quite 

 improbable ; since, if we examine them, we shall find that the extreme 

 difference of all the sixteen measures taken on the two evenings is 



only 



