GREAT REFRACTING TELESCOPE AT ELCHIES, IN MORAYSHIRE. 



391 



As to the subsidiary question, of whether the faint blue burr seen in both 

 telescopes, in the united place of A and B, might have been really composed of 

 two small and close blue stars, it is no slur on the Elchies telescope's defining 

 power, that that point was not settled then. For, even granting for the moment 

 with the most extreme objectors, that A and B now are, and always have been, 

 these two diminutive and close, blue stars, the power of separating and seeing 

 them as such depends, not only on the defining power of the object-glass, but 

 also on the atmospheric definition at the time and place, as well as on the parti- 

 cular observer's eye. There is no need, however, of confining ourselves to gene- 

 ralities, as there are already recorded in this very case, three sets of observations, 

 all made by one and the same observer, viz., myself; i. e., the Tenerifie, in 1856-68, 

 with a 7 2 object-glass; the Elchies, with an 11-inch ; and the Lilburn Tower, with 

 a 6-inch. Of the transcendent defining power of the latter there can be no question, 

 in a good atmosphere ; yet, the atmosphere having been as bad at Lilburn Tower as 

 at Elchies, only a single star was, as at Elchies, suspected to exist ; but in Teneriflfe, 

 10,000 feet above the sea, where the atmospheric definition was exquisite, two 

 stars were perceived at the first glimpse. The same eye therefore, and a medium 

 size of telescope between the other two, joined to a quality which, though good, 

 could hardly have been superior, but a decidedly better atmospheric definition, pro- 

 duced instantly such superior results. What, therefore, might not be the advantage 

 to astronomy of having a large telescope always mounted in an equally well de- 

 fining atmosphere to that of the Tenerififtan Alta Vista ; for evidently five minutes 

 there, on the showing of the objectors themselves, are, for this purpose, better 

 than four whole nights in a worse atmosphere. 



(8.) a PISCIUM, R.A. l'' 54^ 54^; Decl. + 2° 5' 45", January 1, 1862. 



Com- 

 ponents. 



Magni- 

 tude. 





Colour. 



Position. 





Distance 





Date. 



Authority 



A 

 B 



... 







AB 337 23 





5'l2 





1779-80 



HI. 



A 

 ' B 



• ■• 







AB 333 





... 





1802-08 



K\ 



A 

 B 



... 







AB 335 33 





5-43 





1821-93 



H2 and S 



A 

 B 



3-3 



4-8 







AB 336 54 





3-42 





1821-96 



a 



A 



1 ^ 



... 







AB 332 59 (w 



24) 



3-775 (w 



24) 



1830-93 



Bessel. 



1 A 



' . B 



2-8 

 3-9 



Greenish white 



Blue 



.... AB 335 43 





3-64 





1831-16 



2_ 



A 



B 









AB 331 58 (m 



;4) 



3-760 (w 



4) 



1834-85 



Bessel. 



VOL. XXIII. PART 



II. 











5o 





