of Double Stars, 43 



only equal, but Indeed fuperlor, to having its liglit afcenfion 

 and declination given : for, fince it is to be viewed with very 

 high powers, not fuch as fixed inftruments are generally fur- 

 niflied with, the given right afceniion and declination would be 

 of no fervice. We might, indeed, find the ilar by a fixed or 

 equatorial inftrument ; and, taking notice of its fituation with 

 regard to other neighbouring ftars, find, and view it after- 

 wards, by a more powerful telefcope ; but this will nearly 

 amount to the very fame way which here is purfued, with more 

 deliberate accuracy than we are apt to ufe, while we are em- 

 ployed in feeking out an obje£l to look at. 



It will be required, that the obferver (hould be furnifhed 

 with Flamsteed's Atlas Coeleftis, which muft have the jflars 

 marked from the author's catalogue, by a number eafily added 

 to every ftar with pen and ink, as I have done to mine. The 

 catalogue fhould alfo be numbered by an additional column, 

 after that which contains the magnitudes. I hope in fome 

 future editions of the Atlas to fee this method adopted in print, 

 as the advantage of it is very confiderable, both in referring to 

 the catalogue for the place of a ftar laid down in the Atlas, and 

 in finding a flar in the latter whofe place is given in the 

 former. 



I would recommend a precaution to thofe who wifh to exa- 

 mine the clofeft of my double ftars. It relates to the adjufl 

 ment of the focus. Suppofing the telefcope and the obferver 

 long enough out in the open air to have acquired a fettled tem- 

 perature, and the night fufficiently clear for the purpofe ; let 

 the focus of the inflrument be re-adjufted with the utmoft 

 delicacy upon a ftar known to be fingle, of nearly the 

 fame altitude, magnitude, and colour, as the ftar which is ^o 

 be examined, or upon one flar above and another below the 



G 2 fame. 



