Pittsburg dispatch. [volume] (Pittsburg [Pa.]) 1880-1923, 1892-02-21
MOONS OF JUPITER.
One Is Elongated and Keeps One of
Its Poles to the Planet.
THEIR PERIODS OF ROTATION.
Remarkable Geometric Arrangement Of the
Cluster in Hercules.
DISCOVERIES AT LICK OBSERVATORY
WRITTEN FOR THE DISPATCH J

The most generally interesting results re-
Gently reached at Lick Observatory are
those relating to- the motions of the first and
third satellites of Jupiter deduced by Profs.
Schaeberle and Campbell from their OBJ
servations of the past summer with the
great telescope.
Their observations show that the first
satellite of Jupiter (the satellite nearest to
the planet) is of an ellipsoidal shape, with
its longer axis constantly directed to the
planets center, while all the other satel-
Iites are essentially spherical in form. The
ellipsoidal shape may very likely be caused
by the immense tidal forces exerted bv
Jupiter on its nearest attendant The fact
that the longest axis is always directed
toward the planets center shows that this
satellite revolyes once about the primary
in the same time that it revolves once on
its own axis The same fact has also been
shown by the same observers for the third
satellite, though in a very different
way. A long series of drawings of the
faint markings which are sometimes visible
on the very minute disc of the satellite has
been secured and a comDarison of these
drawings has shown that the third satellite
also constantly turns one face toward Jupi-
ter, just as our own moon constantly turns
one face toward the earth Such condi-
tion OF things in the system of Jupiter has
long been suspected (on more or less sufi-
cient testimony but it is now established
for the first time.
Chance for Better Observations
Markings have been seen on the other
satellites also, but not sufficiently well to
prove that they are subject to the same law.
The planet is coming into more favorable
situation year by year, and it very likely
that it may be possible to establish this law
by actual observation for each one of the
satellites separately. These results are of
material Importance in the theory of such
bodies, and they throw much light on the
question of the age of the system of Jupi-
ter. This is not the place to do more than
announce the results of observation. Read
ers who care for more detail are referred to
papers by Profs. Schaeberle and Campbell
in the publications of the Astronomical So
ciety of the Pacific (No 19).
During 1890 and 1891 the globular cluster
of stars in Hercules has been photographed
several times with the great telescope, with
exposure varying from II to 40 minutes.
The cluster has long been known as one of
the most beautiful of the globular groups Of
stars. 1t is composed of a mass of very
minute stars closely packed together with
outlying wisps of stars on its borders. It is
a beautiful object even in small telescopes,
but it requires large telescope to show its
manifold details. Ore of its very remark
able features is a system of three dark chan
els which meet at point and form angles
of about 1900 with each other.
An Arrangement Without Parallel.
These channels or dark lanes were dis
covered by Lord Rosse and make this cluster
especially noteworthy. Their regularity
each other point to some law in virtue OF
which they exist, and interest is at once ex-
cited to discover some analogue or expla-
nation. There is nothing exactly similar to
this in the solar system. The nearest analo-
que is to be found in the dark channels
which separate the bright rings of Saturn
or in the empty spacies in the group Of
minor planets (asterolds). One of ths
nebuIe (the trifd nebule, 6. G. 4,355) pre-
sents even a closer analogy, for it consists
of bright lobes separated from each other by
dark channels which at once suggest the
channels of the cluster in Hercules and
A careful examination of our negatives
showed that not only were the dark lanes
of Lord Rose clearly exhibited, but thai
many other sets of dark channels were to
be seen. We may define dark channel to
be space of considerable length, empty Of
stars, and bordered at least on one side BY
row of stars. In nearly every case there Is
a row of stars on each side. If we call the
of such a set of channelsa Q
center of force, and mark its position on q
chart by q dot, then find no less than 13
such dots or centers on the chart, one Of
which corresponds with the intersection of
the dark channels OF Lord Rosse, and at
each of these dots at least two channels meet
at angles of about 1900 and nearly always
three channels meet at this same angle.
Characteristic Forms of the Cluster.
That is to say the characteristic form Of
this cluster was repeated and insisted upon
over and over again until il was evident
that definite law was acting to produces
this form.
In a globular system or cluster of stars
we may suppose the mass and the dimen-
s1ons OF each one of the individual stars to
be indefinitely small with reference to the
mass and to the dimensions of the whole
system, and we may also suppose the 'clus-
ter to be so far removed from other systems
Of stars that no influence is e1erted by tho
latter upon the motions of the components
of the former. The motions of the constitu-
INT particles of such q system under the in
iuence of gravitation have been mathemat-
callv investigated and they can be de-
;cribed as follows:
The orbit of each one Of the individual
,tars must be an ellipse whose center COIN
tides with the center of gravity of the clus-
Ter. These elliptic orbits may lie in every
conceivable plane and they may be of all
conceivable shapes-from ellipses so nearly
round as to be almost (or quite) circular, to
others so very much extended as to bs
nearly Cor quite) rectilinear.
All Have the Same Periods.
The center of every orbit must coincids
With the center of the cluster ITSELF Each
Individual star revolves once round its orbit
n period which must be the same for all
he stars, no matter what the shape of each
,rbit may be. If it is circle, the star re-
7olves uniformly about the circumference
10 many degrees each day. If the orbit is
! right line, the velocity of the star is
maximum at the center and zero at the e1-
remlty of the line where the star reverses
is outward swing in order to return once
more to the central. If the orbit is an
llipse, more or less elongated, the velocity
S more or less accelerated As the time OF
evolution of all the stars is the same, IL
ollows that at the end of one such period
ach and every star will have returned to
precisely the same situation which 1t occu-
lied at the beginning of the period, and that
his periodic readjustment will perpetuslly
epeat itself
1t seems as if the phenomena were too
omplex to be explained as the effects OF
,ravitation pure aud simple. There IS no .
)riori reason whv other laws of force may
lot govern other systems than our own or
Why such systems may not be involved in
esisting medium. At the same time lt