44 ^^^' Hep SCH el's Catalogue 



lame. Let die phasnomcna of the adjufting ftar be welf 

 attended to; as, whether it be perfedliy round and well de- 

 fined, or affeded with little appendages that frequently keep 

 playing about the image of the ftar, undergoing fmall alte«'a- 

 tions while it paiTes through the field, at other times remain- 

 ing fixed to it during the whole pafTage, Such deceptions may 

 be detefted by turning or unfcrewing the obje6t-gLifs or fpecu- 

 ium a little in its cell, when thofe appendages will be obferved 

 to revolve the fame w^ay. Being thus acquainted with the 

 jmperfeilions as well as perfedlions of the inftrument, and 

 going immediately from the adjufting ftar, which for that 

 reafon alio fhould be as. near as may be,, to- the double flar which, 

 is to be examined, we may hope to be fuccefsful. The aftrc- 

 nomical Mr. Aubert, who did me the honour to follow this 

 method with y Leonis, which he did not find to be double 

 when the telefcope was adjufted by y itfelf, foon perceived the 

 fmall ftar after he had adjufted it upon Regulus. The inilru^ 

 ment, being one of Mr. Doi.lond's bcil 3I feet achroma- 

 tics, fliewed Mr^ Aubert the two flars of y Leonis in very 

 clofe conjundion, or rather one partly hid behind the other- 

 On comparing thefe appearances with my obfervations of that 

 double ftar, w-e muft not be furprifed to find that I place them, 

 at a vifible diftance from each other : for the Newtonian ref' 

 fledors, on the plan of ray 7-feet one,, as I have found, will 

 give a much fmaller image of the ftars than the 3^ feet achro- 

 matic refradors ; wherefore the two ftars, which in refradorsr 

 as it were run into each other, will in the refledor remaia 

 feparate. For this reafon alfo, thofe who only ufe fuch re- 

 fradors muft not be difappointed if they cannot perceive the. 

 26th, 30, 31, 36, 41, 44, 46, 47, 60, 75j 82, 86, and 87th 

 ftars of my firft clafs to be double, 



A 



