ASTRONOMY, 
J. Goodricke, Efq. has determined the periodic variation 
of Algol, or i? Perfei, (obferved by Montanari to be va¬ 
riable,) to be about id. zih. Its greateft brightnefs is of 
the fecond magnitude, and leaftof the fourth. It changes 
from the fecond to the fourth in about three hours and a 
half, and back again in the fame time, and retains its great- 
eft brightnefs for the other part of the time. See the Phil. 
Tranf. 1783. The fame gentleman likewife difcovered 
that (3 Lyrae was fubjeit to a periodic variation. The fol¬ 
lowing is the refult of his obfervations. It completes all 
his phafes in nd. 19b. during which time it undergoes the 
following changes: 1. It is of the third magnitude for 
about two days. 2. It diminifties in about one day and a 
quarter. 3. It is between the fourth and fifth magnitude 
for lefs than a day. 4. It increafesin about two days. 5. 
It is of the third magnitude for about three days. 6 . It di- 
minifties in about one day. 7. It is fomething larger than 
the fourth magnitude for a little lefs than a day. 8. It 
increafes in about one day and three quarters to the firft; 
point, and fo completes a whole period. See the Philcf. 
Tranf. 1785.—He alfo found, that ^ Cephei is fubjedl to 
a periodic variation of 3d. 8h. 37^'. during which time it 
undergoes the following changes: 1. It is at its greateft 
brightnefs about id. 13b. 2. Its diminution is performed 
in about id. i8h. 3. It is at its greateft obfeuration about 
id. 1 ill. 4. It increafes in about thirteen hours. Its great¬ 
eft: and leaft brightnefs is that between the third and fourth, 
and between the fourth and fifth, magnitudes. 
E. Pigott, Efq. has difcovered n Antinoi to be a varia¬ 
ble ftar, with a period of 7d. 4I1. 38'. The changes hap¬ 
pen as follow : 1. It is at its greateft brightnefs 44± hours. 
2. It decreafes 621ft hours. 3. It is at its greateft bright¬ 
nefs sort hours. 4. It increafes 36:+; hours. When mod 
bright it is of the third or fourth magnitude, and when 
leaf! of the third or fourth. 
In the Phil. Tranf. for 1796, Dr. Herfchel has propofed 
a method of obferving the changes that may happen to the 
fixed ftars; with a catalogue of their comparative bright¬ 
nefs, in order to afeertain the permanency of their luftre. 
Dr. Herfchell, in a paper upon the proper motion of the 
folar fyflem, has alfo given a large collection of ftars which 
were formerly feen, but are now loft; alfo a catalogue of 
variable ftars, and of new ftars; and very juftly obierves, 
that it is not eafy to prove that a ftar was never feen be¬ 
fore ; for, though it fhould not be contained in any cata¬ 
logue w’hatever, yet the argument for its former non-ap¬ 
pearance, which is taken from its not having been obfer¬ 
ved before, is only fo far to be regarded, as it can be made 
probable, or almoft certain/ that a ftar would have been 
obferved, had it been vifible. 
There have been various conjectures to account for the 
appearances of the changeable ftars. Maupertuis fuppo- 
fes, that they may have fo quick a motion about their ax¬ 
es, that the centrifugal force may reduce them to flat oblate 
fpheroids, not much unlike a mill-ftone ; that its plane may 
be inclined to the plane of the orbits of its planets, by 
whole attraction the pofition of the body may be altered, 
So that, when its plane palles through the Earth, it may be 
aimed; or entirely invilible, and then become again vifible 
as its broad fide is turned towards 11s. Others have conjec¬ 
tured, that confidcrable parts of their furfaces are covered 
with dark fpots, fo that whpn, by the rotation of the ftar, 
thefe fpots are prefented to us, the ftars become almoft or 
entirely invilible. Others have fuppofed, that thefe ftars 
have very large opaque bodies revolving about and near 
to them, fo as to obfeure them when they come in con¬ 
junction with us. The irregularity of the phafes of fome 
of them fhews the caufe to be variable, and therefore may 
perhaps be bed accounted for, by fuppofing that a great 
part of the body of the ftar is covered with fpots, which 
appear and dilappear like thofe on the Sun’s furface. The 
total difa^pearance of a ftar may probably be the deftruc- 
tion of its fyftem ; and the appearance of a new ftar, the 
creation of a new fyftem of planets. 
With refpeCt to the nature of the fixed ftars, their im- 
3 
menfe diftance precludes 11s from a»n inveffigation of thofe 
particulars from w’hence politive faCts can be deduced. 
What we can gather for certain from their phenomena, is 
as follows : id. That the fixed ftars are greater than our 
Earth ; becaufe, if that was not the cafe, they could not 
be vifible at fuch immenfe diftance. 2dly, That the fixed 
ftars are farther diftant from the Earth than the fartheft of 
the planets. For we frequently find the fixed ftars hid be¬ 
hind the body of the planets: and belidc-s, they have no 
fenfible parallax, which the planets have. 3d»!y, The fix¬ 
ed ftars ftiine with their own light; for they are much far¬ 
ther from the Sun than Saturn, and appear much fmaller 
than Saturn ; but fince, notwithftanding this, they are 
found to ftiine much brighter than that planet, it is evi¬ 
dent they cannot borrow their light from the fame fource 
as Saturn does, viz. the Sun; but, iince we know of no 
other luminous body beft-de the Sun, whence they might 
derive their light, it follows that they ftiine with theirowa 
native light. Belides, it is known, that the more a tele¬ 
fcope magnifies, the lefs is the aperture through which the 
ftar is feen ; and, confequently, the fewer rays it admits in¬ 
to the eye. Now, fince the ftars appear lefs in a telefcope 
which magnifies 200 times, than they do to the naked eye,, 
infomuch that they feem to be only indivifible points, it 
proves at once that the ftars are at immenfe diftances from 
11s, and that they ftiine by their own proper light. If they 
fhone by borrowed light, they would be as invilible with¬ 
out telefcopes as the fatellites of Jupiter are; for the fa- 
tellites appear larger when viewed with a good telefcope 
than the largeft fixed ftars do. Hence, 1. We deduce, that 
the fixed ftars are fo many funs ; for they have all the cha¬ 
racters of funs. 2. That in all probability the ftars are 
not fmaller than our Sun. 3. That it is highly probable 
each ftar is the centre of a fyftem, and has planets or earths 
revolving round it, in the fame manner as round our Sun,, 
i. e. it has opaque bodies illuminated, warmed, and che- 
riflied, by its light and heat. As we have incomparably 
more light from the Moon than from all the ftars together, 
it is abfurd to imagine that the ftars were made for no o- 
ther purpofe than to call a faint light upon the Earth ; efpe- 
cially Iince many more require the aiTiftance of a good te¬ 
lefcope to find them out, than are vifible without that in- 
ftrument. Our Sun is furrounded by a fyftem of planets 
and comets, all which would be invilible from the neareft 
fixed ftar; and, from what we already know of the im¬ 
menfe diftance of the ftars, it is eafy to prove, that the Sun, 
feen from fuch a diftance, would appear no larger than a 
ftar of the firft magnitude. From all this it is highly pro¬ 
bable, that each ftar is a Sun to a, fyftem of worlds moving 
round it, though unfeen by 11s; efpecially as the doCtrine 
of a plurality of worlds is rational, and greatly manifefts- 
the power, the wifdom, and the goodnefs, of the great 
Creator. How immenfe, then, does the univerfe appear! 
Indeed, it muft either be infinite, or infinitely near it. Kep¬ 
ler, it is true, denies that each ftar can have its fyftem of 
planets as ours has; and takes them all to be fixed in the 
fame furface or fphere; urging, that, were one twice or 
thrice as remote as another, it would be twice or thrice as 
fmall, fuppofing their real magnitudes equal; whereas- 
there is no difference in their apparent magnitudes, juftly 
obferved, at all. But to this it is oppofed, that Huygens 
has not only Ihewn, that fires and flames are vifible at dif¬ 
tances where other bodies, comprehended under equal an¬ 
gles, dilappear; but it fhould likewife feem, that the optic 
theorem about the apparent diameters of objects, being 
reciprocally proportional to their diftances from the eye,, 
does only huld while the objeCt has fome fenfible ratio to- 
its diftance. Upon the whole, therefore, the doClrine of 
the fixed ftars, as lately introduced by Dr. Herfchel, not 
only coincides with the opinions of the moft.able mathe¬ 
maticians and philofophers, but has the belt fupport from, 
analogical reafoning, from obvious probability, and from, 
the voluntary teltimony our fenfes. 
As to the motion of the ftars, they are of two kinds ; one- 
called the JirJl, common , or diurnal, motion, arifing from the- 
Earth’s 
