406 PROFESSOR C. PIAZZI SMYTH ON THE 



The two small stars picked up at Elchies may be useful in future inquiries 

 into these conditions, 



(21.) ^ SAGITTiE, R.A. IQi^ 42^ 52S and D. + 18° 47' 57", January 1, 1862. 



°™r . '^^^' Colour. Position. Distance. Date. Authority. 



A ... o , 



B ... AB 304 10 8-83 1781-88 H^. 



A 5-2 



B 9-7 AB 309 15 858 182265 a. 



A ... 



B ... AB314 32 882 1823-69 Hg and S. 



A ... 



B ... AB 318 26 9-81 1829-63 E.^ 



A 57 Green white 



B 8-8 Blue AB 312 50 8-49 1831-10 2. 



A 5 Silvery-white 



B 9 Blue AB312 18(i«;9) 8-6(w9) 1838-67 Cycle. 



A ... Yellowish-white 



B ... Azure 18445 Sestini. 



A ... Yellow(l).., 



B ... Blue(l) 1856-68 AltaVista. 



A 5-2(3) Whitish(3) 



B 9-7(3) Violet (3) AB313 19(m^2) 8-66(tt^l) 



C 15-0(3) Blue (3) AC 250 42 (t'.l) 71-35 (ic»0-5) 1862-73 Elchies. 



In Magnitude, a variation of one magnitude seems probable. 



In Colour, K variable from white to yellowish; but B constant. 



In Position and Distance these stars have been a sore puzzle ever since their 

 first discovery, and are nearly a converse to ^ Cygni, for they form a pair of 

 which hardly any one succeeded during half a century in obtaining a tolerably 

 accordant measure. Differences, indeed, of 14° in angle of position, and 1"*5 in 

 distance, seem to destroy all our accustomed faith in the skill of double star- 

 observers and our belief in the superior closeness or accuracy of their measures : 

 yet all these symptoms of movement of some sort, notwithstanding, one of the 

 most recent (1860) standard published authorities describes the true conclusion 

 to be that the stars are relatively " fixed," and in " optical relationship beyond 

 all reasonable doubt." 



This conclusion is however negatived by the B. A. C. test of proper motion, 

 which in such case would demand a decrease of position to the extent of 21°, and 

 increase of distance to \"-2 in thirty years, a result which the Elchies observation 

 declares emphatically has not taken place. A and B should therefore from this 



