'228 PHILOSOPHICAL TRANSACTIONS. [ANNO I 7 & '2. . 



sense, pass the meridian at the same instant of time. Their distance lias even 

 eluded the attacks of my smallest silk-thread micrometer armed with an excellent 

 power of 460 ; but I shall soon apply my last new instrument to them, not 

 without hopes of success. Now, though I have hitherto not been able to ex- 

 press the distance of the stars of the first class, otherwise than by the propor- 

 tion it bears to their apparent diameters, I think it a very great point gained, 

 that one of my instruments at least (viz. the cross-hair micrometer) has laid hold 

 of them : for their angle of position, I think, is within a very small quantity as 

 well determined as it is in those of the 2d class. This simple but most useful 

 instrument can, by actual measure, discover beyond a doubt a motion in 2 stars 

 that are very close together, though it should amount to no more than a 10th 

 part of a second of a degree, provided that motion be in such a direction that 

 the effect of it be thrown on the angle of position ; wherein, with some of the 

 stars of the first class, it would occasion an alteration of 10, 20, 30, or more 

 degrees. 



I have marked all those stars in my catalogue which have been observed by 

 Mr. Mayer, and other astronomers, with an asterisk (*) affixed to the number, 

 that they may be known ; those with the mark of a dagger (-f~) have been ob- 

 served by different astronomers before Mr. Mayer. Among the stars which are 

 not marked, will be found several that have been observed by Mr. Mayer ; but, 

 on comparing them together, it will be seen, that they are observations of dif- 

 ferent small stars ; for instance, Mr. Mayer (Act. Acad. vol. 4, p. 296) ob- 

 served a small star near Rigel at the distance of l m s . 5 ar in time, and 2' 55".2 

 in difference of declination north preceding Rigel. In my 2d class (the 34th 

 star) we also find Rigel ; but the small star I have observed is one which has not 

 been seen by Mr. Mayer, and is at a distance of no more than 6" 27'". Posi- 

 tion 68° 12' south preceding ; and so on with other stars. 



I have used the expression double-star in a few instances of the 6th class in 

 rather an extended signification : the example of Flamsteed, however, will suf- 

 ficiently authorize my application of the term. I preferred that expression to 

 any other, such as comes, companion, or satellite ; because, in my opinion, it 

 is much too soon to form any theories of small stars revolving round large ones, 

 and therefore I thought it adviseable carefully to avoid any expression that might 

 convey that idea. I am very well persuaded that Flamsteed, who first used the 

 word comes, meant it only in a figurative sense. I shall not fail to take the first 

 opportunity of looking out for those of Mr. Mayer's double-stars which I have 

 not in my catalogue, amounting to 31 ; and also for one I find mentioned in 

 La Connoissance des Temps for 1783, discovered by Mr. Messier. 



