An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

MtOTIONS OF TH'fl, i,'IflCJ) T'AtS. 2T97
1elr of stars in tile M:15ilky Way at five antd a k1tf mil.ions, illcluding' suchl only as are;ilsible in his twenty-feet reflector.
I'itc Gralax)y is supposed to be one of thle umuncrous,nebuhtt,
and tlhe sul of our own solar system to be one of tile stars
whllicl compllose it. It appears comllparati~vely large to us, and
extends entirely round thle hIeavenls, only because we are inl
the nlidst of it, and see it projected in diflerent directions
from us.
[APT]):). II:.
7,otioxs OF THiE F IX143) STARS.-)lSTANTCES —' NATURlt1E.
4-29. IN: 1803, Sir William Hl:orshcl first determined and
annoulced to the world, that thero oxist; among tho stars sepalate syStCe, es, compsed of two stars, revolving about each
other in reg'cullar orbits. Tihese he denominated.Binarz/y Sat's,
to distiniouishi them from other double stars wlere no stuch
motion is detected, and whose proximity to each other llmay
possibl3y arise fiom casual juxtaposition, or firom one being in
the ranlge of the other. At presents, more tlhan a hundred of
tho binary stairs are known, and as the number of suchlt revolutions known among the double stars is constantly increasing
as tfei titles of Comparison increase, it mlay be antciil)atet l that,
in after aces, so large a plroportion of all the double stars -will
be found to possess this character, as to authorize thie belief
that tmhe) universally consist of subordinate sytstems, of whic
the membec s hlave a} revolution aroundl a common center of
gravity. T o'hte periodic tim?.es of the binary stars tre very
various. -While solme (as <.lferulis, and 6 C6oronam) complete
their revolutions in 30 or 40 years, others (as y Virainis) require more than:1.70, anld others still (as G65 Piscium) take ul)
thle long period of 3000 years.x*'.heir orblits alre in general
mtore ccentric than those of thle )lanets. 1That of G(:a1lmma
Virginis, ilmluding thle relative positions of the two compllolnets
* Sm t h's..............................
SI-Iyths's Cycle, L. 1). 300.