Air, Herschel's Catalogue of Double Stars, 41 



24 begins here at 25, and the fame is done with the other 

 clafles. 



Moil: of the double ftars in my firfl: collection are among the 

 number of thofe ftars which have their places determined in 

 Mr. Flamsteed's extenfive catalogue ; but of this colledicn 

 many are not contained in that author's work, I have therefore 

 adopted a method of pointing them out, which it will be prooer 

 to defcribe. 



The finder of my reflector is limited, by a proper diaphragm, 

 to a natural field of two degrees of a great circle in diameter. 

 The interle<51:ion of the crofs wires, in the center of it, points^ 

 out one degree ; and by the eye this degree, or the diilance. 

 from the center to the circumference, may be divided into I, 

 I, I, -1^ ^iid f. Thus we are furnifhed with a meafure which,. 

 though coarfe, is however fufficiently accurate for the purpofe,- 

 here intended ; and which, if more than two degrees are 

 wanted, may be repeated at pleafure. 



In fuch meafures as thefe I have given the diftance of a dou-. 

 ble ftar, whofe place I wanted to point out, from the neareft 

 flar in Flamsteed's Catalogue. And fince, befides the 

 diftance, it is alfo required to have its pofition with regard to 

 the ftarthus referred to, I have ufed the neighbouring ilars for 

 the purpofe of pointing it out. 



The ufefulnefs of this method is fo extenfive, that I fhall be 

 a little more particular in defcribing its application. When a 

 ftar is thus pointed out, as for inftance the 32d in the firll: clafs, 

 where it is faid, '* About | degree f. preceding the 44th Lyncis, 

 *' in a line parallel to Q Urfas majoris and the 39th Lyncis ;" we 

 are to apply one eye to the finder, and placing the 44th Lyncij 

 into. the center of the field, we are to look at;^.Urfae majoris 

 and the 39th Lyncis in the heavens with the other eye by the 



Vol. LXXV. G Uz 



