VOL. LVII.] PHILOSOPHICAL TRANSACTIONS. - 437 



with a telescope of 12 feet length, he discovered in the Pleiades 78 stars, and 

 with longer telescopes many more; but if a telescope of 12 feet length, the 

 aperture of whose object lens was probably less than 2 inches, Increased the 

 number of visible stars in the Pleiades to 78, we may well suppose that with an 

 object lens of 2 feet diameter, they would amount to more than 1000. What 

 this number would be, must depend however on the gradation of real magnitude 

 among the stars of that system, to which there must necessarily be some limit, 

 and it is not therefore improbable that observations of the increase of the 

 number of stars among the Pleiades, &c. with telescopes of larger apertures, 

 especially if this was carried on to very large sizes, might serve to inform us of 

 many circumstances, both with regard to this gradation, and perhaps some other 

 things, that would enable us to judge with more probability concerning the 

 distances, magnitudes, &c. of the stars of our own system. 



If we now imagine a spectator among the Pleiades to take a view of this 

 system from thence, supposing the distance, as before, 57 times the mean 

 distance of our own stars, we should appear to him as a nebulae, in which there 

 would be no star bright enough to be distinguishable by the naked eye; and with 

 a telescope, the aperture of whose object lens was 2 inches, he would hardly be 

 able to distinguish more than half a score stars at the utmost. 



Having hitherto supposed the distances of the stars of our own system to be 

 the same with those of the Pleiades, and examined the appearances according 

 to that hypothesis, let us now, instead of their distances, suppose their 

 magnitudes to be the same. This would make this system, as seen from the 

 Pleiades, to subtend an angle of about 12 degrees instead of 2, and about 

 half a score of the largest stars would be there visible to the naked eye; but a 

 telescope, whose object lens was of 2 inches aperture, would in that case take 

 in almost all the stars belonging to this system of the 4th magnitude and 

 upwards. These appearances fall in less with the general analogy of what we 

 see in the heavens, than the former supposition; but for want of more observa- 

 tions we cannot say this with any certainty: in the mean time however, till we 

 have something further to go upon, it may not perhaps be amiss to take a kind 

 of medium between the 2, and suppose the Pleiades to be at about 20 times the 

 mean distance of the stars belonging to our own system, in which case n will 

 exceed the largest of these, in the proportion of about 8 or 10 to one; or it will 

 exceed the sun, according to our former suppositions of his being of a medium 

 size among 1000 or 350 stars, in one case in the proportion of about 8 or 10 

 thousand, and in the other, about 1000 or 1200 to 1 ; its parallax in the former 

 case being about 36"", and in the latter about H'". 



Mr. M. concludes this inquiry with one observation more, concerning the 

 appearance of the stars of our own system, as seen from great distances. 



