ConftruSlkn of ihe Heavem* 25 c/ 



of Slrius. And, perhaps, in putting it, by the apparent fize 

 of the ilars, at. 600 only, I may have coniiderably under-rated 

 it; but my argument, if that fliouid be the cafe, will be fo 

 much the ftronger. Now to proceed, 



Some of theie round nebulae have others near them, perfectly 

 fimilar in form, colour, and the didribution of flars, but of only 

 half the diameter: aiidtheftarsintiiemfeem to be doubly crowded, 

 and only at about half the diliance from each other : they arc 

 indeed \o fmail as not to be vlfible without the utmoft attention, 

 I fuppofe theie miniature nebulae to be at double the dllfance of 

 the firft. An inifance, equally remarkable and infl:ru6tive, is 

 a cafe where, in the neighbourhood of two fuch nebulae as 

 have been mentioned, I met with a third, fimilar, refolvable, 

 but much fmaller and flfmter nebula. The frars of it are no 

 longer to be perceived ; but a refemblance of colour witli the 

 former two, and its dimlnhhed fize and light, may well per- 

 mit us to place it at full twice the diftance of the fecond, or^ 

 about four or five times that of the firft. And yet the nebu- 

 lofity is not of the milky kind ; nor is it fo much as difficultly 

 refolvable, or colourlefs. Now, in a few of the extended ne- 

 bulcc, the light changes gradually fo as from the refolvable to 

 approach to the milky kind; which appears to me an indica- 

 tion that the milky light of nebula? is owing to their much 

 greater diftance. A nebula, therefore, whofe light is perfedly 

 milky, cannot well be fuppofed to be at lefs than fix or eight 

 thoufand times the diftance of Slrius ; and though the numbers 

 here ailumed are not to be taken otherwife than as very coarfc 

 eftimates, yet an extended nebula, which in an oblique fitua- 

 tion, where it is pofiibly fore-fhortened by one-half, two-thirds, 

 or three- fourths of its length, fubtends a degree or more in 



L 1 -i diameter, 



