, 1876-10-20
sSpots on the Moon.

vor because OF Ine eNluenCe they seeu W
rive of change. One is crater lying
on tbe so-called Sea of Serenity, which
come popular lunar observers regard as
aIo left eve of the Man in the Moon.
Uore there was once deep crater, near
= Seven miles across, q very distinct and
cbvious feature even with the small
toIescope (less than four inches in aper-
tureI nsed by Beer and Nader in form
- their celebrated chart. But ten
Tears ago the skillful astronomer
Schmidt, a selenographer of seleno-
granhers- rs-who has, in fact, given the
Sest energies of his life to moon-gazing
lfound this crater missing. When he
0nnounced the fact to the scientific
world. other astronomers, armed with
vorv powerful instruments, looked for
the crater which had been SO clearly
saen with Madler's small telescope; but
tbouph they found O crater, it was moth
mo like the crater described by Madler.
The present crater is scarcely two miles
in diameter, and only just visible with
nowerful telescopes ;.all around it there
Is a shallow depression, occupying
region about as large as the whole crater
had been before. 1t seems impossible
to doubt that great change has taken
nlace here, and the question arises
whether the change has been produced
bv volcanic activity or otherwise. Sir
John Herschel pronounced somewhat
confidently in favor of the former hypo-
thesis. 1.-THE most plausible coniec-
tnre." said he, "as to the cause of this
disappearance seems to be the filling up
of the crater from beneath by an effu-
sion of viscous lava, which, overhowing
the rim on all sides, may have so flowed
down the outer slope as to efsce its rug
pedness, and convert it into a gradual
declivity, casting no stray shadows"
But how tremendous the volcanic ener-
py required to fill with lava a crater
nearly seven miles in diameter, and
more than half mile deep! The vol
canic hypothesis seems on this account
utterly Incredible, for If such energy
resided in the moons interior, we
should find her whole surface continu-
ally changing. Far more probable
seems the idea that the wall of the crater
has simply fallen in, scattering its frag-
ments over what had been the floor of
the crater. The forces at work on the
moon are quite competent to throw
down steep crater walls like those which
seem formerly 10 have girt about this
deep cavity. Under the tremendous
and long lasting heat Of the lunar mid
day sun, the rock substance of the
moons surface must expand, while dur
; ing the intense cold of the lunar night
corresponding contraction must take
place. Under the influence of this al
ternate expansion and contraction the
strongest Of the crater walls must be
tending to their downfall. Their sub
stance must be gradually crumbling
away. From time to time large masses
must topple over, and occasionally long
ranges Of crater walls must be brought
to the ground. 1t seems conceivable
enough, certainly far more probable
than any other Interpretation which has
been offered, that the crater wall first
missed by Schmidt was destroyed in
this way.
The other favorite region of seleno-
graphers is much larger one-the
walled plain called Plato, and by older
astronomers the Great Black Lake, six
ty miles in diameter, and surrounded
by mountains, some of which rise nearly
$500 yards above the level Of the floor.
According to selenographers, the whole
Of this floor changes in aspect regular
ly during each lunar day-the lunar
day, be it remembered, being equal in
length to what we terrestials term a
long lunar month. In the lunar morn
ing hours the floor is light, during lu-
mar midday it is dark, and in the even
ing it grows light again. The idea Of
selenographers as to the cause OF this
change is that some process of vegeta-
ton takes place over this depressed
-hoor lit lies more than half O mile below
the mean lunar level); or else that va
pors ascend when the suns heat is
poured on the floor and tarnish it some
way, while after midday heat has pass
ed the vapors are re-absorbed and the
surface resumes its former lustre. The
protane, however, urge that the whole
matter is mere effect Of contrast: in
the morning and evening the black
shadows of the surrounding mountains
are thrown on part of the floor, and the
rest BY contrast looks light, whereas,
az midday, the same mountains (which
are white and bright form ring of
ngnt all around the floor, which, there
lore, looks dark by contrast. The sele-
nognphers maintain, on the contrary,
mat they have not been deceived by
contrast, and adbue sub JUDGE lis est.
One can understand that to those who
nave leisure to pore, after the seleno-
graphic fashion, into the details of our
satellites surface, the work must pos
sess certain charm. Though the near
ess OF all the heavenly bodies, the moon
sul lies so far away that every minute
apparent signs of change imply really
important disturbances and though as
Ionomers have given up the idea that
Snere can be life of any sort on the