The Portland daily press. [volume] (Portland, Me.) 1862-1921, 1896-07-11

server placed in it's midst would see a
boundless horizon stretching away from
him on all sides. He would not realizs
the fact that PtoleInaeus was surrounded
moro or less completely by noble circle
of lofty mountains, for these mountains
would be below his horizon. Some of the
peaks ascend one mile, and in certain
cases even two N lies, above the interior
of the plain. AT certain points the
mountain chains will be found inter
rupted by mighty passes. Especially is
his the case on the margin between
prolemaeus and tbs next adjoining
Jailed plain, which is called Alphonsus.
To my mind, however, the most inter-
esting of these objects, as well as perhaps
the most perfect representative of its
class, is the beautiful walled plain named
Plato. This is so we'll placed, and has
such a striking appearance, that it is
probably one of the first objects which
student of lunar topography succeeds in
Identifying No other object Of the same
character happens to lie in it's neighbor-
hood, and consequently, there is but lit
tie difficulty in distinguishing the walled
plain referred to; for it may be remarked
that the aspect of the moon changes so
frequently that the Identification of some
features is at timessa little troublesome.
This partly arises from the never-ending
varieties of light and shade as the moon
changes from day to day.
Where is also another circumstance
which is sometimes apt to puzzle the
beginner, for, owing to what is called
the moons filtration, the face which is
directed toward us is not always exactly
the same. Hence it follows that at
different times the distances of objects
from the circular edge of the moon to
which they are lying nearest will be
found to vary. The difficulties will, how
ever, not prevent the student from read
lily identifying the superb object known
as Plato. 1t lies in the northern region
of the moon, and as our telescopes ex-
hibit the. object inverted, this means that
Plato must be sought at the lower part
OF, tho field.
This walled plain is situated on the
coast line of magnificent lunar sea.
namely, the Mare I'm brium, which may,
perhaps, be described as stupsndous
gulf branching off from the Oceanus
Procellarum. This is, indeed, the re-
gion of the moon toward which we would
specially direct the attention of the
student. There he win find magnificent
examples of the most striking types of
lunar scenery. The floor Plato meas
ures about sixty miles across. 1t may be
said to be fiat, with the exception of GER
tain small Irregularities; bHt the fact
whic oh chiefly strikes the attention of the
observer, and which is specially noticca-
BILE in the photographs, is the unusual
darkness of that floor as compared with
other parts of the moon. The ram part
of mountains which surrounds Plato Is
comparatively perfect. and no more
pleasing lunar picture can BIO beheld
than when this shadows of these noun
tain peaks lis stretched along the dark
central iloor as they do when the sun is
in sueh position that it would just ap-
pear to be rising to lunar inhabitant
who was stationed in the neighborhood
| may mention that the shadows of
mar mountain peaks not only greatly
enhance the beauty of our lunar picture
from spectacular point Of WV, but they
have another Importance. They present
TO the astronomer the only means which
he possesses for measuring the attitudes
of the lunar mountains Ror, as lunar
mountain is more OF less pointed toward
the observer, it's elevation above the sur
facs cannot be attained by direct meas
urements.
We may illustrate the process employed
in the determination of the altitude of
lunar mountain by the operation Of cal
culating the height Of q Flagstaff from
knowing the length of the shallow which
it casts at noon. If the length of that
shadow be measured On certain days,
which will Of course. vary with the lati-
tude of the observer, then the length of
the noontide shadow of the Flagstaff
would not be different from the height
of the flagstaff itself. If the observations
be made on amy other days save those
which have just been mentioned, then
Gn6 l6nRGn OF Gno nOOnUlO6 6uaUOW would
be greater or less than the altitude of the
flagstaff. However, by little calculation,
which any one who has learned mathe-
matics can easily understand, it is posi-
Die from knowing the length of the
shadow and the true altitude of the sun
at'noon on the day in question, to deJer-
mine the height of the flagstaff by which
that shadow has been cast.
We can measure the lengths of the
shadows which are cast by the mountain
peaks on the surface of the moon. Sup
poss, for instance, the shadows were OBJ
served to extend half way across the floor
of Plato, in such case we know that the
length Of the shadow would be about
thirty miles. From our knowledge of
the relative positions of the earth and
the moon we can determine the height of
the sun as 1t would have appeared to a
lamar observer. These facts suffice to
enable US to ascertain the a ltitude of the
corresponding peaks.
The isthmus on whieh Plato is situated