VOL. LXXXVI.] - PHILOSOPHICAL TRANSACTIONS. 713 



kind of limits can be of no real use in the classification of stars. The hypo- 

 thesis of an equality and an equal distribution of stars to which we have referred, 

 is too far from being strictly true to be laid down as an unerring guide in this 

 research. The stars of the 1st and 2d class, when scrupulously examined, evi- 

 dently prove that if we would be accurate, we must admit them, in some degree 

 at least, to be either of different sizes, or placed at different distances. Both 

 varieties undoubtedly take place. This consideration alone is fully sufficient to 

 show, that how much truth soever there may be in the hypothesis of an equal 

 distribution and equality of stars, when considered in a general view, it can be 

 of no service in a case where great accuracy is required. 



Since therefore it appears, that in the classification of stars into magnitudes, 

 there either is no natural standard at all, or at least none that can be satisfac- 

 tory ; it follows, that astronomers who have classed them thus, have referred 

 their size or lustre to some imaginary idea of brightness. The great number of 

 stars indeed which have been placed into every particular class, may assist us to 

 form a kind of confused type in our minds, by which we may be enabled to 

 arrange others ; but how doubtful this must ever remain, we may see from the 

 circumstance of the intermediate expressions that have been introduced. 1.2 m,* 

 for instance, denotes that a star so marked is between the 1st and 2d magnitude. 

 2.1 m signifies the same thing, with an intimation that the star so distinguished 

 is nearly of the 2d magnitude, but partakes still something of the lustre of a 

 star of the 1st order. With stars of the 1st, 2d, and 3d classes there may be 

 some necessity to introduce such sub-divisions ; but how very vague must be the 

 expressions 5 m, 5.6 m, 6.5 m, 6m! In vain have I endeavoured to find a cri- 

 terion for a star of any one of these magnitudes. On looking over, for in- 

 stance, the stars of the 5th order, I found that in the list of other stars which 

 ought to be less bright, because they were marked 5.6 m, 6.5 m, or 6 m, there 

 were many that exceeded the former in brightness, while among those that are 

 set down 5.4 m, 4.5 m, or even 4 m, which ought to be more bright, I found 

 several of a lustre not equal to some of this 5th magnitude, which I was de- 

 sirous to ascertain. We may therefore justly call the method that has been 

 hitherto in use to point out the lustre of stars, a reference to an imaginary 

 standard. 



The inconvenience arising from this unknown, or at least ill ascertained type, 

 to which we are to refer, is such, that now our most careful observations labour 

 under the greatest disadvantage. If any dependence could be placed on the 

 method of magnitudes, it would follow, that no less than 1 1 stars in the con- 

 stellation of the lion, namely, (So-Trg Abed 54 48 72, had all undergone a change 

 in their lustre since Flamsteed's time. For if the idea of magnitudes had been 



* 1 use the letter m in a short way to express the magnitude of the stars. — Orig. 

 VOL. XVII. 4 Y 



