408 ASTRO 
than equal to theirs; and his parallax would be lefs in the 
fame proportion. Suppofing then that the fixed liars are 
of the fame magnitude and brightnel's with the Sun, it is 
no wonder that their parallax fliould hitherto have elcapcd 
obfervation; fince in this cafe it could hardly amount to 
two feconds, and probably not more than one in Sirius 
liimfelf, though he had been placed in the pole of the 
ecliptic ; and, in thole that appear much lefs luminous, as 
y Draconis, which is only of the third magnitude, it could 
hardly be expected to be fenlible with fuch indruments as 
have hitherto been ufed. However, Mr. Michell fug- 
gelts, that it is not impracticable to condruct inftruments 
capable of diltinguifhing even to the twentieth part of a 
fecond, provided the air will admit of that degree of ex- 
adtnefs. This ingenious writer apprehends that the quan¬ 
tity of light which we receive from Sirius, does not ex¬ 
ceed the light we receive from the lead fixed ftar of the 
lixth magnitude, in a greater ratio than that of icoo to i, 
nor lefs than that of 400 to 1 ; and the fmalier flat s of the 
fecond magnitude feem to be about a mean proportional 
between the other two. Hence the whole parallax of the 
lead fixed flars of the fixth magnitude, fuppofing them of 
the fame fize and native brightnel's with the Sun, fliould be 
from about 2'" to 3'", and their didance from about eight 
to twelve million times that of the Sun: and the parallax 
of the fmalier ftars of the fecond magnitude, upon the 
fame fuppolition, Ihoitld be about 12'", and their diftance 
about two million times that of the Sun. 
This author alio imagines, that, from the apparent fitu- 
atisn of the flars in the heavens, there is the greateft pro¬ 
bability that the flars are collected together in cinders in 
foine places, where they form a kind ot fydems, whilll in 
ethers there are either few or none of them ; whether this 
difpodtion be owing to their mutual gravitation, or to fome 
other law or appointment of the Creator. Hence it may 
be inferred, that Inch double dais, Sec. as appear toconlill 
of two or more dars placed very near together, do really 
condd of dars placed near together, and under the influ¬ 
ence of fome general law : and he proceeds to inquire whe¬ 
ther, if the dars be collected into fydems, the Sun does 
not likewife make one of fome fydem, and which fixed 
ftars thofe are that belong to the fame fydem with him. 
Thofe dars, he apprehends, which are found in cinders, 
and furrounded by many others at a fmall didance from 
them, belong probably to other fydems, and not to ours. 
And thofe Itars, which are furrounded with nebuke, are 
probably only very large dars which, on account of their 
fuperior magnitude, are lingly vifible, while the others, 
which compofe the remaining parts of the fame fydem, 
are fo fmall as to efcape our fight. And thofe nebulae in 
which we can difeover either none or only a few dars, even 
with the affidance of the bed telefcopes, are probably 
fydems that arc dill more didant than the red. See Philof. 
Tranf. vol.lvii. p. 234, &c. 
The didance of the (tar y Draconis appears, by Dr. 
Bradley’s obfervations, to be at lead 400,000 times that of 
the Sun, and the didance of the neared fixed filar riot lefs 
than 40,000 diameters of the Earth’s annual orbit: that 
is, the dillance from the Earth, of the former at lead 
3S,coo,000,000,000 miles, and the latter not lefs than 
7,600,000,000,000 miles. Asthefe didances are immenfe- 
ly great,' it may both be annrfing, and help to a clearer 
and more familiar idea, to compare them with the velo¬ 
city of fome moving body, by which they may be meafured. 
The fwifteft motion we know of, is that ot light, which 
pafles from the Sun to the Earth in about eight minutes; 
and yet this would be above lix years traverflng the fird 
fipace, and near a year and a quarter in patting from the 
neared fixed dar to the Earth. But a cannon-ball, mo¬ 
ving on a medium at the rate of about twenty miles in a 
minute, would be 3,800,000 years in pading from 7 Dra¬ 
conis to the Earth, and 76.0,000 years palling from the 
neared fixed (tar. Sound, which moves at the rate of 
about thirteen miles in a minute, would be 3,600,000 years 
traverfing the former didance, and 1,128,000 in pnffing 
N O M Y. 
through the latter. The celebrated Huygens pur fined fpe- 
dilations of this kind fo far, as to believe it not impolfi- 
ble, that there may be dars at fuch inconceivable didan¬ 
ces, that their light has not yet reached the Earth lince 
its creation. Dr. Halley has alfo advanced, what hefavs 
fieems to be a metaphyfical paradox (Philof. Tranf. No. 
ccclxiv. or Abr. vol.vi. p.148), viz. that the number of 
fixed dars mud be more than finite, and fome of them 
more than at a finite didance from others: and Addifon 
has judly obferved, that this thought is far from being 
extravagant, wheu we conlider, that the univerfe is the 
work ot infinite power, prompted by infinite goodnefs, and 
having an infinite fpace to exert itlelf in ; fo tl»at our ima¬ 
gination can fiet no bounds to it. 
Kepler lias alfo made a very ingenious obfiervation upon 
the magnitudes and didances of the fixed dars. He ob- 
fierves, that there can be only thirteen points upon the fur- 
face of a fiphere as far didaut from each other as from the 
centre; and, fuppoling the neared fixed (tars to be as far 
from each other as from the Sun, he concludes, that there 
can be only thirteen dars of the fird magnitude, hence, 
at twice that didance from the Sun, there may be placed 
four times as many, or fifty-two; at three times that dif¬ 
tance, nine times as many, or 117 ; and fo on. Thefe num¬ 
bers will give pretty nearly the number of Itars of the fird, 
fecond, third, &c. magnitudes. Dr. Halley further re¬ 
marks, that, if the number of dars be finite, and occupy 
only a part of fpace, the outward dars would be continu¬ 
ally attracted towards thofe which are within, and in pro- 
cels of time they would coalefcq and unite into one. But, 
if the number be infinite, and they occupy an infinite fpace, 
all the parts would be nearly in equilibrio, and confequent- 
ly each fixed dar, being drawn in oppolite directions, would 
keep its place, or move on till it had found an equilibri¬ 
um. Phil. Tranf. No. ccclxiv. 
In contemplating the magnitudes of the dars, they ap¬ 
pear to be very different from one another; which diffe¬ 
rence may probably arife, partly from a diverlity in their 
real magnitude, but principally from their didances, which 
are certainly very different. To the bare eye, the dars 
appear of fome fendble magnitude, owing to the glare of 
light arifing from the numberlefs reflections from the ae¬ 
rial particles about the eye : this makes us imagine the 
dars to be much larger than they would appear, if we flaw 
them only by the few rays which come direCtly from them, 
fo as to enter our eyes without being intermixed with c- 
thers. Any perfon may be fendble of this, by looking 
at a dar of the fird magnitude through a long narrow tube; 
which, though it takes in as much of the fky as would 
hold a thoufand fuch dars, (carcely renders that one vifible. 
The dars, on account of their apparently-various fizes, 
have been didributed into feveral clades of magnitudes. 
The fird clafs, or dars of the fird magnitude, are thole 
that appear larged, and may probably be neared to us. 
Next to thefe, are thofe of the fecond magnitude; and fo 
on to the fixth, which comprehends the fmalled dars vi¬ 
fible to the naked eye. All beyond thefe, that can be 
perceived by the help of telefcopes, are called telefcopic 
dars. Not that all the dars of each clafs appear judly of 
the fame magnitude ; there being great latitude in this re- 
fpeCt; and thofe of the fird magnitude appearing almofl 
all different in ludre and iize. There are alfo other dars, 
of intermediate magnitudes, which adronomers cannot 
refer to one clafs rather than another, and therefore they 
place them between tiie two. Procyon, for indance, which 
Ptolemy makes of the fird magnitude, and Tycho of the 
fecond, Flamdead lays down as between the fird and fe¬ 
cond. So that, indead of fix magnitudes, we may fay there 
are almod as many orders of dars, as there are dars ; fo 
great ft variation being obfervable in the magnitude, co¬ 
lour, and brightnefs, of them. 
There feems to be little chance of difeovering with cer¬ 
tainty the real fize of any of the fixed liars; we mud there¬ 
fore be content with an approximation, deduced from their 
parallax, if this fliould ever be really found; and the 
quantity 
