Evening star. [volume] (Washington, D.C.) 1854-1972, 1882-08-12
The Boundaries Of Astronomy.

Prof. Ball in the Contemporary Review.
The star sweeps along through our system
with stupendOus velocity. Now there can be no
doubt that if the star were permanently to re-
tain this velocity, it would in the course of time
travel right across our system, and, after
leaving our system, would retreat into the
depths of infinite space. Is there any power
adequate to recall this star from the voyage to
infnity? We know Of none, unless it be the
attraction of the stars or other bodies Of our
sidereal system. 1t therefore becomes q mat
ter OF calculation to determine whether the at
traction of all the material bodies Of our
sidereal system could be adequate, even with
universal gravitatiOn, to recall q body which
seems bent on leaving that system with We
lOcity of 200 miles per second. This interesting
problem has been discussed by Prof. Newcomb,
whose calculations We shall here follow. In the
first place, we require to make some estimate of
the dimensions of the sidereal system. i'm order
to see whether 1t seems likely that this star can
ever be recalled. The number of stars NAV be
taken at 1OO OO0, 600, which is probably double
as many as the number wee see with our best
telescopes. The masses of the stars may be
taken as on the average five times as great as
the mass OF the sun. The distribution of the
stars is suggested by the constitution of the
milky way. One hundred million stars are pre-
sumed to be disposed Ia q fiat circular LAYER of
such dimensions that raw of light would REQUIRE
81. 600 years to traverse one diameter Assuming
the ordinary law OF gravitatiOn, it is now easy
to compute the efficiency of such an arrange
ment in attempting to recall moving star. The
whole question turns on certain critical velo-
city OF Is miles q second. II star darted
through the system We have just been consider
ing with velocity less than IS miles a second.
then, after that star had moved for a certain dis
lance. the attractive power Of the system would
gradually bend the path of the star round, and
force the star to return to the system If.
q fioa af fhn OF dor
no circumstances more than 25 miles a second,
then, suppOsing the system to have the charac-
ter we have described, that system might
be always the same. The stars might
must always remain in the vicinity Of our present
system. and our whole sidereal system might
be an isolated object in space, just as our solar
system is an isolated object In the extent of the
sldereal system We have, however, seen that
for one star at all events the velocity is no less
than 200 miles second. II this star dash
through the system, then the attractions of all
the bodies in the system will unite In one
grand effort to recall the wanderer This
attraction must, to some extent be acknowl-
edged: the speed Of the wanderer must grad
ually diminish as he recedes into space; bat that
speed Will never be lessened sufficiently to brng
the star back again. As the star retreats further
and further, the potency of the attraction will
decrease, but owing to the velocity Of the star
being over 25 miles q second, the attraction can
never overcome the velocity; so that the star
seems destined to escape This calculation is
Of course. founded on our assumption as to the
total mass of the stars and other bodies which
form our sidereal system. That estimate was
founded on liberal, indeed very liberal. in-
depreciation OF the evidence winicn our tee-
scopes have afforded. But it NAV still fall short
OF the ruth. There may be more than hundred
million starsfn our system: their average weight
may be more than five times the weight of our
SUM- But unless the assumption we have made
Is enormously short of the truth, our inference
cannot be challenged