244- Mr, Herschel on the 
T 
half the given field of view, it will be — :r B, the bafe of the 
y'— — - 
cone. And — — d , will be an expreifion for vp, in terms 
of vs, which is the mutual diftance of the fcattered ftars. 
Then having — - ~ n 3 -f 1 »* + | n, we may find n ; whence 
2 dn - d, 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 fo confiderable as 
very materially to affect the conclufions, I (hall, on account of 
the greater convenience, make ufe of the fir ft. 
We inhabit the planet of a far belonging to a Compound Nebula 
of the third form, 
I fhall now proceed to ihew that the ftupendous fidereal fyftem 
we inhabit, this extenfive ftratum and its fecondary branch, 
confifting 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 
aftual furvey of the boundaries of our fidereal fyftem, which 
I have plainly perceived, as far as I have yet gone round it, 
every where terminated, and in moft 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 fufficiently 
.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 (V), and thefe were 
continued for many minutes, fo that in one quarter of an hour s 
time there paffed no lefs than 1 16000 ftars through the field of 
{d) See the table of Gages, p.235. 
view 
