24^ Mr, Herschel ou the 



T 

 half the given field of view, it will be —=: B, the bafe of the 



\/~i 



cone. And — —^—d, will bean expreflion for vp, in terms 



of «yj-, which is the mutual diftance of the fcattered flars. 



Then having — — n^ j^ I n^ ■\- 1 ;?, we may find n ; whence 



idn - ^, the vifual ray, will be obtained. 



The refult of this arrangement gives a fhorter ray than that 

 of the former ; but fince the difference is not {o confiderable as 

 very materially to affe^Sl the conclufions, I (hall, on account of 

 the greater convenience, make ufe of the firft. 



We inhabit the -planet of a Jlar belonging to a Compound 'Nebula 



of the third for tn, 



I fhall now proceed to fliew that the flupendous fidereal lyiLem 

 we inhabit, this extenlive ftratum and its fecondary branch, 

 confifthig of many millions of ftars, is, in all probability, a 

 detached Nebula. In order to go upon grounds that feem to me 

 to be capable of great certainty, they being no lefs than an 

 ii£lual furvey of the boundaries of our iidereal fyflem, which 

 I have plainly perceived, as far as I have yet gone round it, 

 every where terminated, and in mofl places very narrowly too, 

 it will be proper to fhew the length of my founding line, if I 

 may fo call it, that it may appear whether it was fufticiently 

 long for the purpofe. 



In the moft crowded part of the milky way I have had fields 

 of view that contained no lefs than 588 ftars (^), and thefe were 

 continued for many minutes, fo that in one quarter of an hour's 

 time there pafled no lefs than 1 16000 ftars thiough the field of 



(-V) See the table of Gages, p. 235. 



view 



