371 ) 



XXVIII. — On the great Refracting Telescope at Elchies, in Morayshire, and its 

 Powers in Sidereal Ohservation. By Professor C. Piazzi Smyth. 



(Read December 1862 and March 1863.) 



PART A. — Instrumental Details, ..... Pages 371-380 

 PAET B. — Observational Particulars, .... 380-413 



PART C— General Deductions, ..... 413-418 



Part A. — 1. Introduction to Instrumental Details. 



The following pages contain an account of a few double-star measures which, 

 by the kind permission of J. W. Grant, Esq., of Elchies, in Morayshire, I was 

 enabled to make there in September 1862, with his large and equatorially 

 mounted refracting telescope ; and as that instrument is altogether the best and 

 most powerful of its kind which has hitherto been erected in Scotland, such a 

 trial of its capabilities, and the first which has been published, will undoubtedly 

 have a peculiar interest for the Royal Society of Edinburgh. 



The object-glass of the telescope is 11 inches in diameter, or rather its clear 

 aperture, for the glass discs themselves may be a little more ; while the next 

 largest in Scotland, that recently acquired by the Glasgow Observatory, under 

 its present able director. Professor Grant, is not more than 9 inches ; and the 

 chief object-glass of the Royal Observatory of Edinburgh, or that of the Meridian 

 Transit Instrument, only Q\ inches aperture. The light, therefore, of the Elchies 

 telescope is, comparatively, * transcendent ; and to enable this feature to be em- 

 ployed with the best effect upon his favourite stellar pursuits of earlier years in 

 India, where extreme accuracy of measurement was always one of his chief 

 desiderata, Mr Grant spared no expense in securing for the Elchies instru- 

 ment an unusually efficient and well made equatorial mounting, fully provided 

 with clockwork motion and micrometrical apparatus. 



The order for the construction of this instrument would appear to have been 

 given about the year 1849, a period when Mr Grant, though still in India, was 

 just about to bring to a close his long service of forty-four years of continued 

 official residence there : and it seems to have been commenced immediately ; 



* It would not be right to ignore that both England and Ireland have object-glasses of 12 inches 

 in diameter ; that the Russian Observatory of Pulkova has possessed for a quarter of a century, and 

 used with great profit to exact astronomy, an object-glass of 1 5 inches in diameter ; and that, in 

 addition to Paris, the astronomers of the United States have now in employment one of the same 

 size, and also one even of 18 inches in diameter, the normal size for a new generation, with similar 

 advantageous results. 



VOL. XXIII. PART II. 5 I 



