358° Precedings of Learned Societies. 
mew Nebule, Nebulous Stars, Planetary 
Nebule, and Clufters of Stars, with Re- 
marks on the Conftruction of the Heavens,” 
obferves, that ¢* it has hitherto been the 
chief employment of the phyfical aftrono- 
mer to fearch for new celeftial objeéts, 
whatfoever might be their nature or con- 
dition; but our ftock of materials is now fo 
increaied, that we fhouid begin to arrange 
them more fcientifically.”? In dividing 
the different parts of which the fidereal 
heavens are compoled, in proper clafles, 
Dr. Herfchel is obliged to examine the 
nature of the various celeftial objects that 
have been hitherto difcovered, in order to 
arrange them in a manner molt conform- 
able to their conftru@tion. He firf? treats 
of INSULATED STaRs. lt might (fays 
he) be expected, that the folar fyftem 
would ftand foremoft in the lift, whereas, 
by treating of infulated ftars, we feem, as 
it were, to overlook one of the great com- 
ponent parts of the univerfe. It will, 
however, appear that this very fyfem, 
magnificent as it is, can only rank as a 
fingle individual belonging to the {pecies 
which we are going to confider.”’ 
By calling a ftar infulated, Dr. Herfchel 
does not mean to denote its being totally 
unconnected with all other ftars or fyftems ; 
but, when ftars are fituated at fuch im- 
menfe diftances from each other as our 
Sun, Arcturus, Capella, Lyra, Sirius, and 
numberlefs others, we think that we may 
look upon them as fufficiently out of the 
reach of mutual attraGtions, to deferve the 
name of infulated ftars. For it is afcer- 
tained by computation, that fuppofing the 
earth’s orbit, as is highly probable, does 
not extend more than an angle of one fe- 
cond of a degree, when feen from Sirius, 
thea the Sun and Sirius, if the maffes are 
equal, would not fall together in lefs than 
thirty-three millions of years, even though 
they were not impeded by many contrary 
atiractions of other neighbouring infulated 
ftars. A ftar thus fiiuated may certainly 
deferve to be called infulated, and of this 
kind our Sun is probably one. . 
From the detached fituation of infulated 
ftars, it appears that they are capable of 
being centers of extenfive planetary fyf- 
tems; and from analogy we may fuppofe, 
that every one of them is attended with 
planets, fatellites, and numerous comets; 
though there is good reafon for believing 
that we can only look for folar fyfiems 
among infulated ftars. 
. The rext part of the conftruétion of the 
heavens which our aftronomer confiders, 
4 
[ May 1, 
is the union of two flars, that are formed 
together into one fyftem, by the laws of 
attraction: thefe he denominates—II. Br- 
NARY SIDEREAL SYSTEMS, or DOUBLE 
STaRS. Ifa fiar be fituated at any dif- 
tance behind another, and but little de- 
viating from the line in which the firft is 
feen, there would be the appearance of a 
double ftar, but they would not form a 
binary fyfiem. If, however, two ftars 
fhould be really fituated near each other, 
and at the fame time fo far infulated as 
not to be materially affected by the attrac- 
tions of neighbouring ftars, they will then 
compofe a feparate fyftem, and remain 
united by the bond of their mutual gravi- 
tation towards each other. This fhould 
be called a real double ftar ; and any two 
ftars that are thus mutually conneéted, 
form a binary fidereal” fyftem. 
Dr. Herfchel fhews, that two ftars may 
be fo connetted at to perform circles, or ~ 
fimilar ellipfes, round their common centre 
of gravity. And in this cafe they will 
always move in dire€tions oppofite and pa- 
rallel to ecch other, and their fyftem, if 
not deftroyed by fome foreign influence, 
will remain permanent. Hence arifes an 
effential difference between the conftruc- 
tion of folar and fidereal fyftems. In the 
former is a ponderous attractive center, 
by which all the planets, &c. are kept in 
their orbit ; but m the latter, the ftars of 
which they are compofed move round an 
empty center, to which they are neverthe- 
lefs as firmly bound as the planets to their 
mafly one. Such indeed is the cafe of the 
earth and moon, which, in their montbly 
revolutions, move round a center without 
a body placed in if; and the fame may be 
faid of the fun and each planet. 
Dr. Herfchel next enters into a very 
ingenious and fatisfaétory calculation, to 
prove that no Infulated ftars, of nearly 
equal fize and diftance, can appear double 
to us ;—that cafual fituations will not ac- 
count for the multiplied phenomena of 
double ftars, and that con@quently their 
exiftence muft be owing to the influence 
of fome gerera! law of nature, fuch as 
gravitation ; and he means, hereafter, to 
fhew that many of them have actually 
changed their ftuation with regard to each 
other, in a progreffive courfe, denoting a 
periodical revoiution round each other ; 
and that the motion of fome of them is di- 
rect, while that of others is retrograde. 
- Dr. Herfchel then proceeds—III. To. 
TRIPLE, QUADRUBLE, QUINTUPLEs 
and MULTIPLE STARS, and fhews, pei 
that 
