The sun. [volume] (New York [N.Y.]) 1833-1916, 1896-05-17

many respects rcsembled tho physical cnndi
tion which the planet Saturn has ut present
II II be asked why our earth should hav,
passed through those stages Of transformation
by which II has changed from its primeva
condition down 10 the form in which We nov
know II, while Saturn Is still In such an early
stage Of development, the answer Is no doubt
to bc found in the circumstance that saturn
II a vast globe. while our ccrth is CO npara
lively II small one. We need only call attention
to he somewhat rite fact that II small body
cools down moro quickly than n large one. The
earth and saturn. both highly heated in the
beginning, have each been cooling down ever
since; the earth, being com parntively small
has parted so freely with its heat that II has
assumed the form which we now know. sat
urn, on the other hand, being n very large
tody, has but slowly parted with It's heat, ana
consequently still retains vast stores In com
parison with ;hc present state OF the earth.
IL would thus seem that in the present condi-
ton of the globe of Saturn we have Il picture
OF what our earth may once have been like.
1t also seems probable that, aS in the course OF
ages Saturn gradually parts with It's heat. n
time will at length cone when tho water at
present In the clouds which surround " viii
be collected into oceans on Its surface.
Though IL seems almost certain that saturn
Is n highly heated globe. yet II Is not heated
sufficiently to radiate forth light of It's own;
all the light which We receive from thence Ia
merely reflected sunlight. There is album
dant proof of this In various ways. 1t Is, Tor
example, demonstrated In an interesting ma4-
ncr by the fact that the globe of saturn
appears quite black where the shadow OF the
ring ia cast upon II. This. of course. would
not have been the case II the globe had re-
tanned any of its original luminosity.
Thu thapprnnpn pf Saturn and his SVStpm
present problems Of the deepest interest to as
tronomcrs of every class. Especially has the
structure of the ring given rise 10 questions
which have taxed alike the highest powers of
the observing astronomer and of the accom-
plished mathematician. The mechanical char.
actcr of the ring might AZ the first glance ap.
pear to lie II comparatively simple matter. IL
might he thought that each of the two bright
rims vas n broad thin belt of some solid ma.
terial. ana after a little reflection n mechanl-
cal difficulty of the gravest character will he
seen to present itself. For think of the two
halves of which each ring is composed. Each
such half is IA stupcndous arch, an arch which
has to withstand the attraction of the ponder
Gus glcbe in the centre. 1t is not difficult to
calculate the strain to which the materials of
an arch of more than 100, 900 miles span would
be subjected. Engineers are well accustomed
to the notion that it Is impossible for them
to erect an arch which has n span beyond II
certain limit. That limit Is dictated by the cir
that the pressure upon the stones
or other materials of which the arch is built
increases with every increase of the span. Con-
sequently n point would be sometimes reached
when the pressure to which the stones are sub
jected Is so great that any further increase in
span would be attended with the danger that
the structure would collapse with its own
weight. This consideration defines the limit
of the arch which could be constructed out Of
materials.
We can calculate the pressure that would
have to be withstood by the materials in nm
arch such rs that made by one-half of Saturn's
ring. 1t is quite easy TO prove that this press
ure would be so great that even IL the mate
rails were many thousands of times tougher
than the toughest steel or any other known
substance, 1t would be utterly impossible for
tho ringto resist the tendency to collapse. No
doubt the strain on the structure would he
somewhat lightencd by tho fact that the ring
is spinning round rapidly. The centrifugal
force thence arising must to a certain extent
neu.ralize the effect of the attraction of the
planet. This circumstance. though 1t may
lessen. yet It does not remove the difficulty,
for the ring has a very considerable width. II
the centrifugal force were so adjusted as to
neutraliHe the s'r''ho III 'h' Va
the ring, It would be too great for the inner
portion, whiie IL would not DO great enough
for the outer portion. Looked at in whatever
way We please. 1t would seem quite impossible,
on mechanical principles, that each ring OF
Saturn would be composed of n thin belt OF
solid material.
The explanation OF the character Of this
curious structure was first given by the late
Prof. J. Clark Maxwell. He conducted this
memorable research by means of that instru'
ment which is often more subtle than The fele.
scope OF the astronomer mean the pen of
the mathematician. He thus showed that the
rings of Saturn must be composed OF myriads
of little objects. each so minute that II Is quite
impossible for us to see II separately, at Its
present distance from the earth. These little
objects are. however. in such incalculable
myriads, and they lie so close togethe-. that
we can see the mighty shoals which they form.
though we are not able t" discriminate the In
divldual members. By this superstition the
NHW