WEST LONGITUDE 90 deg. TO 60 deg.
SCHUBERT.--This ring-plain, about 46 miles in diameter, situated on the
N.E. side of the Mare Smythii, is too near the limb to be well observed.
NEPER.--Though still nearer the limb, this walled-plain, 74 miles in
diameter, is a much more conspicuous object. It has a lofty border and a
prominent central mountain, the highest portion of a range of hills which
traverses the interior from N. to S.
APOLLONIUS.--A ring-plain, 30 miles in diameter, standing in the
mountainous region S. of the Mare Crisium. There is a large crater on the
S.W. wall, and another, somewhat smaller, adjoining it on the N. There
are many brilliant craters in the vicinity.
FIRMICUS.--A somewhat larger, more regular, but, in other respects, very
similar ring-plain, N.W. of the last. Some distance on the W., Madler
noted a number of dark-grey streaks which apparently undergo periodical
changes, suggestive of something akin to vegetation. They are situated
near a prominent mountain situated in a level region.
AZOUT.--A small ring-plain, connected with the last by a lofty ridge. It
is the apparent centre of many other ridges and valleys which radiate
from it towards the N.W. and the Mare Crisium. There is a central
mountain, not an easy telescopic object, on its dusky floor.
CONDORCET.--A very prominent ring-plain, 45 miles in diameter, situated
on the mountainous S.W. margin of the Mare Crisium. It is encircled by a
lofty wall about 8000 feet in height. The dark interior of this and of
the three preceding formations render them easily traceable under a high
angle of illumination.
HANSEN.--A ring-plain, 32 miles in diameter, on the W. border of the Mare
Crisium N. of Condorcet. Schmidt shows a central mountain and a terraced
wall.
ALHAZEN.--This ring-plain, rather smaller than the last, is the most
northerly of the linear chain of formations, associated with the
highlands bordering the S.W. and the W. flanks of the Mare Crisium. It
has a central mountain and other minor elevations on the floor. There is
a little ring between Alhazen and Hansen, never very conspicuous in the
telescope, which is plainly traceable in good photographs.
EIMMART.--A conspicuous ring-plain with bright walls on the N.W. margin
of the Mare Crisium. The E. border attains a height of 10,000 feet above
the interior, which, according to Schmidt, has a small central mountain.
There is a rill-like valley on the E. of the formation.
ORIANI.--An irregular object, 32 miles in diameter, somewhat difficult to
identify, N.W. of the last. There is a conspicuous crater on the N. of
it, with which it is connected by a prominent ridge.
PLUTARCH.--A fine ring-plain W. of Oriani, with regular walls, and,
according to Neison, with two central mountains, only one of which I have
seen. Both this formation and the last are beautifully shown in a
photograph taken August 19, 1891, at the Lick Observatory, when the
moon's age was 15 d. 10 hrs.
SENECA.--Rather smaller than Plutarch. Too near the limb for satisfactory
observation. Schmidt shows two considerable mountains in the interior.
The position of this object in Schmidt's chart is not accordant with its
place in Beer and Madler's map, nor in that of Neison.
HAHN.--A ring-plain, 46 miles in diameter, with a fine central mountain
and lofty peaks on the border, which is not continuous on the S. There is
a large and prominent crater on the E.
BEROSUS.--A somewhat smaller object of a similar type, N. of Hahn, but
with a loftier wall. There is a want of continuity also in the border,
the eastern and western sections of which, instead of joining, extend for
some distance towards the S., forming a narrow gorge or valley. Outside
the S.E. wall there is a small crater, and some irregular depressions on
the E. The minute central mountain is only seen with difficulty under a
low evening sun. The bright region between Hahn and Berosus and the
western flank of Cleomedes is an extensive plain, devoid of prominent
detail, and which, according to Neison, includes an area of 40,000 square
miles.
GAUSS.--A large, and nearly circular walled-plain, 111 miles in diameter,
situated close to the N.W. limb, and consequently always foreshortened
into a more or less elongated ellipse. But for this it would be one of
the grandest objects in the first quadrant. Under the designation of
"Mercurius Falsus" it received great attention from Schroter, who gives
several representations of it in his _Selenotopographische Fragmente_,
which, though drawn in his usual conventional style, convey a juster idea
of its salient features than many subsequent drawings made under far
better optical conditions. The border, especially on the W., is very
complex, and is discontinuous on the S., where it is intersected by more
than one pass, and is prolonged far beyond the apparent limits of the
formation. The most noteworthy feature is the magnificent mountain chain
which traverses the floor from N. to S. It is interesting to watch the
progress of sunset thereon, and see peak after peak disappear, till only
the great central boss and a few minute glittering points of light,
representing the loftier portions of the chain, remain to indicate its
position. Madler expatiates on the sublime view which would be obtained
by any one standing on the highest peak and observing the setting sun on
one side of him and the nearly "full" earth on the other; while beneath
him would lie a vast plain, shrouded in darkness, surrounded by the
brilliantly illuminated peaks on the lofty border, gradually passing out
of sunlight. In addition to the central mountain range, there are some
large rings, craters, hillocks, &c., on the floor; and on the inner slope
of the W. border there is a very large circular enclosure resembling a
ring-plain, not recorded in the maps. Schmidt shows a row of large
craters on the outer slope of the E. border. Of these, one is very
conspicuous under a low evening sun, by reason of its brilliant walls and
interior. In the region between Gauss and Berosus is a number of narrow
steep ridges which follow the curvature of the E. wall.
STRUVE.--A small irregularly-shaped formation, open towards the S.,
forming one of the curious group of unsymmetrical enclosures associated
with Messala. Its dark floor and a small dusky area on the N. indicate
its position under a high sun.
CARRINGTON.--A small ring-plain, belonging to the Messala group,
adjoining Schumacher on the N.W.
MERCURIUS.--This formation is 25 miles in diameter. A small crater stands
on the S.E. section of the wall. There is a longitudinal range in the
interior, and on the W. and N.W. the remains of two large walled-plains,
the more westerly of which is a noteworthy object under suitable
conditions. A short distance S. is a large, irregular, and very dark
marking. On the N., lies an immense bright plain, extending nearly to the
border of Endymion.
WEST LONGITUDE 60 deg. TO 40 deg.
TARUNTIUS.--Notwithstanding its comparatively low walls, this ring-plain,
44 miles in diameter, is a very conspicuous object under a rising sun.
Like Vitello and a few other formations, it has an inner ring on the
floor, concentric with the outer rampart, which I have often seen nearly
complete under evening illumination. There is a small bright crater on
the S.E. wall, and a larger one on the crest of the N.E. wall, with a
much more minute depression on the W. of it, the intervening space
exhibiting signs of disturbance. The upper portion of the wall is very
steep, contrasting in this respect with the very gentle inclination of
the _glacis_, which on the S. extends to a distance of at least 30 miles
before it sinks to the level of the surrounding country, the gradient
probably being as slight as 1 in 45. Two low dusky rings and a long
narrow valley with brilliant flanks are prominent objects on the plain E.
of Taruntius under a low evening sun.
SECCHI.--A partially enclosed little ring-plain S. of Taruntius, with a
prominent central mountain and bright walls. There is a short cleft
running in a N.E. direction from a point near the E. wall. Schmidt
represents it as a row of inosculating craters.
PICARD.--The largest of the craters on the surface of the Mare Crisium,
21 miles in diameter. The floor, which includes a central mountain, is
depressed about 2000 feet below the outer surface, and is surrounded by
walls rising some 3000 feet above the Mare. A small but lofty ring-plain,
Picard E, on the E., near the border of the Mare, is remarkable for its
change of aspect under different angles of illumination. A long curved
ridge running S. from this, with a lower ridge on the west, sometimes
resemble a large enclosure with a central mountain. Still farther S.,
there is another bright deep crater, _a_, with a large low ring adjoining
it on the S., abutting on the S.E. border of the Mare. Schroter bestowed
much attention on these and other formations on the Mare Crisium, and
attributed certain changes which he observed to a lunar atmosphere.
PEIRCE.--This formation, smaller than Picard, is also prominent, its
border being very bright. There is a central peak, which, though not an
easy object, I once glimpsed with a 4 inch Cook achromatic, and have seen
it two or three times since with an 8 1/2 inch Calver reflector. A small
crater, detected by Schmidt, which I once saw very distinctly under
evening illumination, stands on the floor at the foot of the W. wall.
Peirce A, a deeper formation, lies a little N. of Peirce, and has also,
according to Neison, a very slight central hill, which is only just
perceptible under the most favourable conditions. Schmidt appears to have
overlooked it.
PROCLUS.--One of the most brilliant objects on the moon's visible
surface, and hence extremely difficult to observe satisfactorily. It is
about 18 miles in diameter, with very steep walls, and, according to
Schmidt, has a small crater on its east border, where Madler shows a
break. It is questionable whether there is a central mountain. It is the
centre of a number of radiating light streaks which partly traverse the
Mare Crisium, and with those emanating from Picard, Peirce, and other
objects thereon, form a very complicated system.
MACROBIUS.--This, with a companion ring on the W., is a very beautiful
object under a low sun. It is 42 miles in diameter, and is encircled by a
bright, regular, but complex border, some 13,000 feet in height above the
floor. Its crest is broken on the E. by a large brilliant crater, and its
continuity is interrupted on the N. by a formation resembling a large
double crater, which is associated with a number of low rounded banks and
ridges extending some distance towards the N.W., and breaking the
continuity of the _glacis_. The W. wall is much terraced, and on the N.W.
includes a row of prominent depressions, well seen when the interior is
about half illuminated under a rising sun. The central mountain is of the
compound type, but not at all prominent. The companion ring, Macrobius C,
is terraced internally on the W., and the continuity of its N. border
broken by two depressions. There is a rill-valley between its N.E. side
and Macrobius.
CLEOMEDES.--A large oblong enclosure, 78 miles in diameter, with massive
walls, varying in altitude from 8000 to 10,000 feet above the interior.
The most noteworthy features in connection with the circumvallation are
the prominent depressions on the W. wall. Under a rising sun, when about
one-fourth of the floor is in shadow, three of these can be easily
distinguished, each resembling in form the analemma figure. There are two
other curious depressions at the S.W. end of the formation. On the dark
steel-grey floor are two irregular dusky areas, and a narrow but bright
central mountain, on which, according to Schmidt, stand two little
craters. There are two ring-plains on the S.W. quarter, and a group of
three associated craters on the N. side, one of which (A) Schroter
believed came into existence after he commenced to observe the formation,
a supposition that has been shown by Birt and others to be very
improbable.
TRALLES.--A large irregular crater, one of the deepest on the visible
surface of the moon, situated on the N.E. wall of Cleomedes. There is a
crater on its N. wall, and, according to Schmidt, some ridges and three
closely associated craters on the floor.
BURCKHARDT.--This object, situated on an apparent extension of the W.
wall of Cleomedes, is 35 miles in diameter, with a lofty border, rising
on the E. to an altitude of nearly 13,000 feet. It has a prominent
central mountain and some low ridges on the floor, which, together with
two minute craters on the S.W. wall, I have seen under a low angle of
morning illumination. It is flanked both on the E. and W. by deep
irregular depressions, which present the appearance of having once been
complete formations.
GEMINUS.--A fine regular ring-plain, 54 miles in diameter, nearly
circular, with bright walls, rising on the E. to a height of more than
12,000 feet, and on the opposite side to nearly 16,000 feet above the
floor. Their crest is everywhere very steep, and the inner slope is much
terraced. There is a small but conspicuous mountain in the interior; N.
of which I have seen a long ridge, where Schmidt shows some hillocks. Two
fine clefts are easily visible within the ring, one running for some
distance on the S.E. side of the floor, mounting the inner slope of the
S.W. border to the summit ridge (where it is apparently interrupted), and
then striking across the plain in a S.W. direction. Here it is
accompanied for a short distance by a somewhat coarser companion, running
parallel to it on the N. The other cleft occupies a very similar position
on the N.W. side of the floor at the inner foot of the wall. On several
occasions, when observing this formation and the vicinity, I have been
struck by its peculiar colour under a low evening sun. At this time the
whole region appears to be of a warm light brown or sepia tone.
BERNOUILLI.--A very deep ring-plain on the W. side of Geminus. Under
evening illumination its lofty W. wall, which rises to a height of nearly
13,000 feet above the floor, is conspicuously brilliant. This formation
exhibits a marked departure from the circular type, being bounded by
rectilineal sides. The inner slope of the W. wall is slightly terraced.
The border on the S. is much lower than elsewhere, as is evident when the
formation is on the evening terminator. On the N. is the deep crater
Messala _a_.
NEWCOMB.--The most prominent of a group of formations standing in the
midst of the Haemus Mountains. Its crest is nearly 12,000 feet above the
floor, on which there are some hills.
MESSALA.--This fine walled-plain, nearly 70 miles in diameter, is, with
its surroundings, an especially interesting object when observed under a
low angle of illumination. Its complex border, though roughly circular,
displays many irregularities in outline, due mainly to rows of
depressions. The best view of it is obtained when the W. wall is on the
evening terminator. At this phase, if libration is favourable, the
manifold details of its very uneven and apparently convex floor are best
seen. On the S.W. side is a group of large craters associated with a
number of low hills, of which Schmidt shows five; but I have seen many
more, together with several ridges between them and the E. wall. I noted
also a cleft, or it may be a narrow valley, running from the foot of the
N.W. wall towards the centre. On the floor, abutting on the N.E. border,
is a semicircular ridge of considerable height, and beyond the border on
the N.E. there is another curved ridge, completing the circle, the wall
forming the diameter. This formation is clearly of more ancient date than
Messala, as the N.E. wall of the latter has cut through it. Where Messala
joins Schumacher there is a break in the border, occupied by three deep
depressions.
SCHUMACHER.--A large irregular ring-plain, 28 miles in diameter,
associated with the N. wall of Messala, and having other smaller rings
adjoining it on the E. and N. The interior seems to be devoid of detail.
HOOKE.--Another irregular ring-plain, 28 miles in diameter, on the N.E.
of Messala. There is a bright crater of considerable size on the S.W.,
which is said to be more than 6000 feet in depth, and, according to
Neison, is visible as a white spot at full. There is a smaller crater on
the slope of the N.W. wall.
SHUCKBURGH.--A square-shaped enclosure on the N. of the last, with a
comparatively low border. It has a conspicuous crater at its N.W. corner.
BERZELIUS.--A considerable ring-plain of regular form, with low walls and
dark interior, on which there is a central peak, difficult to detect.
FRANKLIN.--A ring-plain, 33 miles in diameter, which displays a
considerable departure from the circular type, as the border is in great
part made up of rectilineal sections. Both the W. and N.E. wall is much
terraced, and rises about 8000 feet above the dark floor, on the S. part
of which there is a long ridge. There is a bright little isolated
mountain on the plain E. of the formation, and a conspicuous craterlet on
the N.W. An incomplete ring, with a very attenuated border, abuts on the
S. side of Franklin.
CEPHEUS.--A peculiarly shaped ring-plain, 27 miles in diameter. The E.
border is nearly rectilineal, while on the W., the wall forms a bold
curve. There is a very brilliant crater on the summit of this section,
and a central mountain on the floor. The W. wall is much terraced. W. of
Cepheus, close to the brilliant crater, there is a cleft or narrow valley
running N. towards Oersted.
OERSTED.--An oblong formation with very low walls, scarcely traceable on
the S.E., except when near the terminator. There is a conspicuous crater
on the N.W. side of the floor, and a curious square enclosure, with a
crater on its W. border, abutting on the N.E. wall.
CHEVALLIER.--An inconspicuous object enclosed by slightly curved ridges.
It includes a deep bright crater. On the N. is a low square formation and
a long ridge running N. from it. Just beyond the N.E. wall is the fine
large crater, Atlas A, with a much smaller but equally conspicuous crater
beyond. A has a central hill, which, in spite of the bright interior, is
not a difficult feature.
ATLAS.--This, and its companion Hercules on the E., form under oblique
illumination a very beautiful pair, scarcely surpassed by any other
similar objects on the first quadrant. Its lofty rampart, 55 miles in
diameter, is surmounted by peaks, which on the N. tower to an altitude of
nearly 11,000 feet. It exhibits an approach to a polygonal outline, the
lineal character of the border being especially well marked on the N. The
detail on the somewhat dark interior will repay careful scrutiny with
high powers. There is a small but distinct central mountain, south of
which stands a number of smaller hills, forming with the first a circular
arrangement, suggestive of the idea that they represent the relics of a
large central crater. Several clefts may be seen on the floor under
suitable illumination, among them a forked cleft on the N.E. quarter, and
two others, originating at a dusky pit of irregular form situated near
the foot of the S.E. wall, one of which runs W. of the central hills, and
the other on the opposite side. A ridge, at times resembling a light
marking, extends from the central mountain to the N. border. During the
years 1870 and 1871 I bestowed some attention on the dusky pit, and was
led to suspect that both it and the surrounding area vary considerably in
tone from time to time. Professor W.H. Pickering, observing the formation
in 1891 with a 13 inch telescope under the favourable atmospheric
conditions which prevail at Arequipa, Peru, confirmed this supposition,
and has discovered some very interesting and suggestive facts relating to
these variations, which, it is hoped, will soon be made public. On the
plain a short distance beyond the foot of the _glacis_ of the S.E. wall,
I have frequently noted a second dusky spot, from which proceeds, towards
the E., a long rill-like marking. On the N. there is a large formation
enclosed by rectilineal ridges. The outer slopes of the rampart of Atlas
are very noteworthy under a low sun.
HERCULES.--The eastern companion of Atlas, a fine ring-plain, about 46
miles in diameter, with a complex border, rising some 11,000 feet above a
depressed floor. There are few formations of its class and size which
display so much detail in the shape of terraces, apparent landslips, and
variation in brightness. In the interior, S.E. of the centre, is a very
conspicuous crater, which is visible as a bright spot when the formation
itself is hardly traceable, two large craterlets slightly N. of the
centre, and several faint little spots on the east of them. The latter,
detected some years ago by Herr Hackel of Stuttgart, are arranged in the
form of a horse-shoe. There are two small contiguous craters on the S.E.
wall, one of which, a difficult object, was recently detected by Mr. W.H.
Maw, F.R.A.S. The well-known wedge-shaped protuberance on the S. wall is
due to a large irregular depression. On the bright inner slope of the N.
wall are manifest indications of a landslip.
ENDYMION.--A large walled-plain, 78 miles in diameter, enclosed by a
lofty, broad, bright border, surmounted in places by peaks which attain a
height of more than 10,000 feet above the interior, one on the W.
measuring more than 15,000 feet. The walls are much terraced and exhibit
two or three breaks. The dark floor appears to be devoid of detail.
Schmidt, however, draws two large irregular mounds E. of the centre, and
shows four narrow light streaks crossing the interior nearly parallel to
the longer axis of the formation.
DE LA RUE.--Notwithstanding its great extent, this formation hardly
deserves a distinctive name, as from the lowness of its border it is
scarcely traceable in its entirety except under very oblique light.
Schmidt, nevertheless, draws it with very definite walls, and shows
several ridges and small rings in the interior. Among these objects, a
little E. of the centre, there is a prominent peak.
STRABO.--A small walled-plain, 32 miles in diameter, connected with the
N. border of the last.
THALES.--A bright formation, also associated with the N. side of De la
Rue, adjoining Strabo on the N.E. Schmidt shows a minute hill in the
interior.
There are several unnamed formations, large and small, between De la Rue
and the limb, some of which are well worthy of examination.
WEST LONGITUDE 40 deg. TO 20 deg.
MASKELYNE.--A regular ring-plain, 19 miles in diameter, standing almost
isolated in the Mare Tranquilitatis. The floor, which includes a central
mountain, is depressed some 3000 feet below the surrounding surface.
There are prominent terraces on the inner slope of the walls. Schmidt
shows no craters upon them, but Madler draws a small one on the E., the
existence of which I can confirm.
MANNERS.--A brilliant little ring-plain, 11 miles in diameter, on the
S.E. side of the Mare Tranquilitatis. There appears to be no detail
whatever in connection with its wall. It has a distinct central mountain.
About three diameters distant on the S.W. there is a bright crater,
omitted by Madler and Neison.
ARAGO.--A much larger formation, 18 miles in diameter, N. of the last,
with a small crater on its N. border, and exhibiting two or three spurs
from the wall on the opposite side. The inner slopes are terraced, and
there is a small central mountain. There are two curious circular
protuberances on the Mare E. of Arago, which are well seen when the W.
longitude of the morning terminator is about 19 deg., and a long cleft,
passing about midway between them, and extending from the foot of the E.
wall to a small crater on the edge of the Mare near Sosigenes. Another
cleft, also terminating at this crater, runs towards Arago and the more
northerly of the protuberances.
CAUCHY.--A bright little crater, not more than 7 or 8 miles in diameter,
on the W. side of the Mare Tranquilitatis, N.E. of Taruntius. It has a
peak on its W. rim considerably loftier than the rest of the wall, which
is visible as a brilliant spot at sunrise long before the rest of the
rampart is illuminated. On the S. there are two bright longitudinal
ridges ranging from N.E. to S.W. These stand in the position where Neison
draws two straight clefts. The Cauchy cleft, however, lies N. of these,
and terminates, as shown by Schmidt, among the mountains N.E. of
Taruntius. I have seen it thus on many occasions, and it is so
represented in a drawing by M.E. Stuvaert (_Dessins de la Lune_). There
is a number of minute craters and mounds standing on the S. side of this
cleft, and many others in the vicinity.
JANSEN.--Owing to its comparatively low border, this is not a very
conspicuous object. It is chiefly remarkable for the curious arrangement
of the mountains and ridges on the S. and W. of it. There is a bright
little crater on the S. side of the floor, and many noteworthy objects of
the same class in the neighbourhood. The mountain arm running S., and
ultimately bending E., forms a large incomplete hook-shaped formation
terminating at a ring-plain, Jansen B. The ridges in the Mare
Tranquilitatis between Jansen B. and the region E. of Maskelyne display
under a low sun foldings and wrinklings of a very extraordinary kind.
MACLEAR.--A conspicuous ring-plain about 16 miles in diameter. The dark
floor includes, according to Madler, a delicate central hill which
Schmidt does not show. Neison, however, saw a faint greyish mark, and an
undoubted peak has been subsequently recorded. I have not succeeded in
seeing any detail within the border, which in shape resembles a triangle
with curved sides.
ROSS.--A somewhat larger ring-plain of irregular form, on the N.W. of the
last. There are gaps on the bright S.W. border and a crater on the S.E.
wall. The central mountain is an easy feature.
PLINIUS.--This magnificent object reminds one at sunrise of a great
fortress or redoubt erected to command the passage between the Mare
Tranquilitatis and the Mare Serenitatis. It is 32 miles in diameter, and
is encompassed by a very massive rampart, rising at one peak on the E. to
more than 6000 feet above the interior, and displaying, especially on the
S.E., and N., many spurs and buttresses. The exterior slopes at sunrise,
and even when the sun is more than 10 deg. above the horizon, are seen to
be traversed by wide and deep valleys. The S. _glacis_ is especially
broad, extending to a distance of 10 or 12 miles before it runs down to
the level of the plain. The shape of the circumvallation, when it is
fully illuminated, approximates very closely to that of an equilateral
triangle with curved sides. There are two bright little craters on the
outer slope, just below the summit ridge on the S.E., and another,
larger, on the N. wall, in which it makes a prominent gap. The interior
is considerably brighter than the surface of the surrounding Mare, and, a
little S. of the centre, includes two crater-like objects with broken
rims. These assume different aspects under different conditions of
illumination, and it is only when the floor is lighted by a comparatively
low morning sun, that their true character is apparent. On the N.W.
quarter of the interior are two smaller distinct craters, and a square
arrangement of ridges. On the N.E. there are some hillocks and minor
elevations. The Plinius rills form an especially interesting system, and
under favourable conditions may be seen in their entirety with a good 4
inch refractor, about the time when the morning terminator passes through
Julius Caesar. They consist of three long fissures, originating amid the
Haemus highlands, on the S. side of the Mare Serenitatis, and diverging
towards the W. The most southerly commences S.S.E. of the Acherusian
promontory (a great headland, 5000 feet high, at the W. termination of
the Haemus range), and, following a somewhat undulating course, runs up
to the N. side of Dawes. Under a low evening sun, I have remarked many
inequalities in the width of that portion of it immediately N. of
Plinius, which appear to indicate that it is here made up of rows of
inosculating craters. The cleft north of this originates very near it,
passes a little S. of the promontory, and runs to the E. edge of the
plateau surrounding Dawes. The third and most northerly cleft begins at a
point immediately N. of the promontory, cuts through the S. end of the
well-known Serpentine ridge on the Mare Serenitatis, and, after following
a course slightly concave to the N., dies out on the N. side of the
plateau. This cleft forms the line of demarcation between the dark tone
of the Mare Serenitatis and the light hue of the Mare Tranquilitatis,
traceable under nearly every condition of illumination, and prominent in
all good photographs.
DAWES.--A ring-plain 14 miles in diameter, situated N.W. of Plinius, on a
nearly circular light area. Its bright border rises to a height of 2000
feet above the Mare, and includes a central mountain, a white marking on
the E., and a ridge running from the mountain to the S. wall. There are
two closely parallel clefts on the N. side of the plateau running from E.
to W., that nearer Dawes being the longer, and having a craterlet
standing upon it about midway between its extremities. At its W.
termination there is a crater-row running at right angles to it. The
light area appears to be bounded on the E. by a low curved bank.
VITRUVIUS.--A ring-plain 19 miles in diameter with bright but not very
lofty walls, situated among the mountains near the S.W. side of the Mare
Serenitatis. It is surrounded by a region remarkable for its great
variability in brightness. There is a large bright ring-plain on the W.,
with a less conspicuous companion on the S. of it.
MARALDI.--A deep but rather inconspicuous formation, bounded on the W. by
a polygonal border. A small ring-plain with a central mountain is
connected with the S.W. wall; and, running in a N. direction from this,
is a short mountain arm which joins a large circular enclosure with a low
broken border standing on the N. side of the Mare Tranquilitatis.
LITTROW.--A peculiar ring-plain, rather smaller than the last, some
distance N. of Vitruvius, on the rocky W. border of the Mare Serenitatis.
It is shaped like the letter D, the straight side facing the W. There is
a distinct crater on the N. wall. On the N.W. it is flanked by three
irregular ring-plains, and on the S.E. by a fourth. Neison shows two
small mountains on the floor, but Schmidt, whose drawing is very true to
nature, has no detail whatever. A fine cleft may be traced from near the
foot of the E. wall to Mount Argaeus, passing S. of a bright crater on
the Mare E. of Littrow. It extends towards the Plinius system, and is
probably connected with it.
MOUNT ARGAEUS.--There are few objects on the moon's visible surface which
afford a more striking and beautiful picture than this mountain and its
surrounding heights with their shadows a few hours after sunrise. It
attains an altitude of more than 8000 feet above the Mare, and at a
certain phase resembles a bright spear-head or dagger. There is a well-
defined rimmed depression abutting on its southern point.
ROMER.--A prominent formation of irregular outline, 24 miles in diameter,
situated in the midst of the Taurus highlands. It has a very large
central mountain, a crater on the N. side of the floor, and terraced
inner slopes. Some distance on the N. is another ring, nearly as large,
with a crater on its S. rim, and between this and Posidonius is another
with a wide gap on the S. and a crater on its N. border. One of the most
remarkable crater-rills on the moon runs from the E. side of Romer
through this latter ring, and then northwards on to the plain W. of
Posidonius. Under suitable conditions, it can be seen as such in a 4 inch
achromatic. It is easily traceable as a rill in a photograph of the N.
polar region of the moon taken by MM. Henry at the Paris Observatory, and
recently published in _Knowledge_.
LE MONNIER.--A great inflection or bay on the W. border of the Mare
Serenitatis S. of Posidonius. Like many other similar formations on the
edges of the Maria, it appears at one time or other to have had a
continuous rampart, which on the side facing the "sea" has been
destroyed. In this, as in most of the other cases, relics of the ruin are
traceable under oblique light. A fine crescent-shaped mountain, 3000 feet
high, stands near the S. side of the gap, and probably represents a
portion of a once lofty wall. It will repay the observer to watch the
progress of sunrise on the whole of the W. coast-line of the Mare up to
Mount Argaeus.
POSIDONIUS.--This magnificent ring-plain is justly regarded as one of the
finest telescopic objects in the first quadrant. Its narrow bright wall
with its serrated shadow, the conspicuous crater, the clefts and ridges
and other details on the floor, together with the beautiful group of
objects on the neighbouring plain, and the great Serpentine ridge on the
E., never fail to excite the interest of the observer. The
circumvallation, which is far from being perfectly regular, is about 62
miles in diameter, and, considering its size, is not remarkable for its
altitude, as it nowhere exceeds 6000 feet above the interior, which is
depressed about 2000 feet below the surrounding plain. Its continuity,
especially on the E., is interrupted by gaps. On the N., the wall is
notably deformed. It is broader and more regular on the W., where it
includes a large longitudinal depression, and on the N.W. section stand
two bright little ring-plains. On the floor, which shines with a
glittering lustre, are the well-marked remains of a second ring, nearly
concentric with the principal rampart, and separated from it by an
interval of nine or ten miles. The most prominent object, however, is the
bright crater a little E. of the centre. This is partially surrounded on
the W. by three or four small bright mountains, through which runs in a
meridional direction a rill-valley, not easily traced as a whole, except
under a low sun. There is another cleft on the N.E. side of the interior,
which is an apparent extension of part of the inner ring, a transverse
rill-valley on the N., a fourth _quasi_ rill on the N.W., and a fifth
short cleft on the S. part of the floor. Between the principal crater and
the S.E. wall are two smaller craters, which are easy objects. Beyond the
border on the N., in addition to Daniell, are four conspicuous craters
and many ridges.
CHACORNAC.--This object, connected with Posidonius on the S.W., is
remarkable for the brilliancy of its border and the peculiarity of its
shape, which is very clearly that of an irregular pentagon with linear
sides. I always find the detail within very difficult to make out. Two or
more low ridges, traversing the floor from N. to S., and a small crater,
are, however, clearly visible under oblique illumination. Schmidt draws a
crater-rill, and Neison two parallel rills on the floor,--the former
extends in a southerly direction to the W. side of Le Monnier.
DANIELL.--A bright little ring-plain N. of Posidonius. It is connected
with a smaller ring-plain on the N.W. wall of the latter by a low ridge.
BOND, G.P.--A small bright ring-plain 12 miles in diameter, W. of
Posidonius. Neison shows a crater both on the N. and S. rim. Schmidt
omits these.
MAURY.--A bright deep little ring-plain, about 12 miles in diameter, on
the W. border of the Lacus Somniorum. It is the centre of four prominent
hill ranges.
GROVE.--A bright deep ring-plain, 15 miles in diameter, in the Lacus
Somniorum, with a border rising 7000 feet above a greatly depressed
floor, which includes a prominent mountain.
MASON.--The more westerly of two remarkable ring-plains, situated in the
highlands on the S. side of the Lacus Mortis. It is 14 miles in diameter,
has a distinct crater on its S. wall, and, according to Schmidt, a crater
on the E. side of the floor.
PLANA.--A formation 23 miles in diameter, closely associated with the
last. Neison states that the floor is convex and higher than the
surrounding region. It has a triangular-shaped central mountain, a
crater, and at least three other depressions on the S.W. wall where it
joins Mason.
BURG.--A noteworthy formation, 28 miles in diameter, on the Mare, N. of
Plana. The floor is concave, and includes a very large bright mountain,
which occupies a great portion of it. The interior slopes are prominently
terraced, and there are several spurs associated with the _glacis_ on the
S. and N.E. A distinct cleft runs from the N. side of the formation to
the S.E. border of the Lacus Somniorum, which is crossed by another
winding cleft running from a crater E. of Plana towards the N.E.
BAILY.--A small ring-plain, N. of Burg, flanked by mountains, with a
large bright crater on the W. The group of mountains standing about
midway between it and Burg are very noteworthy.
GARTNER.--A very large walled-plain with a low incomplete border on the
E., but defined on the W. by a lofty wall. Schmidt shows a curved crater-
row on the W. side of the floor.
DEMOCRITUS.--A deep regular ring-plain, about 25 miles in diameter, with
a bright central mountain and lofty terraced walls.
ARNOLD.--A great enclosure, bounded, like so many other formations
hereabouts, by straight parallel walls. There is a somewhat smaller
walled-plain adjoining it on the W.
MOIGNO.--A ring-plain with a dark floor, adjoining the last on the N.E.
There is a conspicuous little crater in the interior.
EUCTEMON.--This object is so close to the limb that very little can be
made of its details under the most favourable conditions. According to
Neison, there is a peak on the N. wall 11,000 feet in height.
METON.--A peculiarly-shaped walled-plain of great size, exhibiting
considerable parallelism. The floor is seen to be very rugged under
oblique illumination.
WEST LONGITUDE 20 deg. TO 0 deg.
SABINE.--The more westerly of a remarkable pair of ring-plains, of which
Ritter is the other member, situated on the E. side of the Mare
Tranquilitatis a little N. of the lunar equator. It is about 18 miles in
diameter, and has a low continuous border, which includes a central
mountain on a bright floor. From a mountain arm extending from the S.
wall, run in a westerly direction two nearly parallel clefts skirting the
edge of the Mare. The more southerly of these terminates near a
depression on a rocky headland projecting from the coast-line, and the
other stops a few miles short of this. A third cleft, commencing at a
point N.E. of the headland, runs in the same direction up to a small
crater near the N. end of another cape-like projection. At 8 h. on April
9, 1886, when the morning terminator bisected Sabine, I traced it still
farther in the same direction. All these clefts exhibit considerable
variations in width, but become narrower as they proceed westwards.
RITTER.--Is very similar in every respect to the last. A curved rill
mentioned by Neison is on the N.E. side of the floor and is concentric
with the wall. On the N. side of this ring-plain are three conspicuous
craters, the two nearer being equal in size and the third much smaller.
SCHMIDT.--A bright crater at the foot of the S. slope of Ritter.
DIONYSIUS.--This crater, 13 miles in diameter, is one of the brightest
spots on the lunar surface. It stands on the E. border of the Mare, about
30 miles E.N.E. of Ritter. A distinct crater-row runs round its outer
border on the W., and ultimately, as a delicate cleft, strikes across the
Mare to the E. side of Ritter. Both crater-row and cleft are easy objects
in a 4 inch achromatic under morning illumination.
ARIADAEUS.--A bright little crater of polygonal shape, with another
crater of about one-third the area adjoining it on the N.W., situated on
the rocky E. margin of the Mare Tranquilitatis, N.E. of Ritter. A short
cleft runs from it towards the latter, but dies out about midway. A
second cleft begins near its termination, and runs up to the N.E. wall of
Ritter. E. of this pair a third distinct cleft, originating at a point on
the coast-line about midway between Ariadaeus and Dionysius, ends near
the same place on the border. There is a fourth cleft extending from the
N. side of a little bay N. of Ariadaeus across the Mare to a point N.W.
of the more northerly of the three craters N. of Ritter. At a small
crater on the S. flank of the mountains bordering the little bay N. of
Ariadaeus originates one of the longest and most noteworthy clefts on the
moon's visible surface, discovered more than a century ago by Schroter of
Lilienthal. It varies considerably in breadth and depth, but throughout
its course over the plain, between Ariadaeus and Silberschlag, it can be
followed without difficulty in a very small telescope. E. of the latter
formation, towards Hyginus (with which rill-system it is connected), it
is generally more difficult. A few miles E. of Ariadaeus it sends out a
short branch, running in a S.W. direction, which can be traced as a fine
white line under a moderately high sun. It is interesting to follow the
course of the principal cleft across the plain, and to note its progress
through the ridges and mountain groups it encounters. In the great Lick
telescope it is seen to traverse some old crater-rings which have not
been revealed in smaller instruments. About midway between Ariadaeus and
Silberschlag it exhibits a duplication for a short distance, first
detected by Webb.
DE MORGAN.--A brilliant little crater, 4 miles in diameter, on the plain
S. of the Ariadaeus cleft.
CAYLEY.--A very deep bright crater, with a dark interior, N. of the last,
and more than double its diameter. There is a second crater between this
and the cleft.
WHEWELL.--Another bright little ring, about 3 miles in diameter, some
distance to the E. of De Morgan and Cayley.
SOSIGENES.--A small circular ring-plain, 14 miles in diameter, with
narrow walls, a central mountain, and a minute crater outside the wall on
the E.; situated on the E. side of the Mare Tranquilitatis, W. of Julius
Caesar. There is another crater, about half its diameter, on the S.,
connected with it by a low mound. This has a still smaller crater on the
W. of it.
JULIUS CAESAR.--A large incomplete formation of irregular shape. The wall
on the E. is much terraced, and forms a flat "S" curve. The summit ridge
is especially bright, and has a conspicuous little crater upon it. On
the W. is a number of narrow longitudinal valleys trending from N. to S.,
included by a wide valley which constitutes the boundary on this side.
The border on the S. consists of a number of low rounded banks, those
immediately E. of Sosigenes being traversed by several shallow valleys,
which look as if they had been shaped by alluvial action. There is a
brilliant little hill at the end of one of these valleys, a few miles E.
of Sosigenes. The floor of Julius Caesar is uneven in tone, becoming
gradually duskier from S. to N., the northern end ranking among the
darkest areas on the lunar surface. There are at least three large
circular swellings in the interior. A long low mound, with two or three
depressions upon it, bounds the wide valley on the E. side.
GODIN.--A square-shaped ring-plain, 28 miles in diameter, with rounded
corners. The bright rampart is everywhere lofty, except on the S., is
much terraced, and includes a central mountain. On the S. a curious
trumpet-shaped valley, extending some distance towards the S.W., and
bounded by bright walls, is a noteworthy feature at sunrise. There are
other longitudinal valleys with associated ridges on this side of the
formation, all running in the same direction. There is a large bright
crater outside the border on the N.E., and, between it and the wall,
another, smaller, which is readily seen under a high sun.
AGRIPPA.--A ring-plain 28 miles in diameter on the N. of the last, with a
terraced border rising to a height of between 7000 and 8000 feet above
the floor, which contains a large bright central mountain and two craters
on the S. The shape of this formation deviates very considerably from
circularity, the N. wall, on which stands a small crater, being almost
lineal. On the W., at a distance of a few miles, runs the prominent
mountain range, extending northwards nearly up to the E. flank of Julius
Caesar, which bounds the E. side of the great Ariadaeus plain. Between
this rocky barrier and Agrippa is a very noteworthy enclosure containing
much minute detail and a long straight ridge resembling a cleft. A few
miles N. of Agrippa stands a small crater; at a point W. of which the
Hyginus cleft originates.
SILBERSCHLAG.--A very brilliant crater, 8 or 9 miles in diameter,
connected with the great mountain range just referred to. The Ariadaeus
cleft cuts through the range a few miles N. of it. This neighbourhood at
sunrise presents a grand spectacle. With high powers under good
atmospheric conditions, the plain E. of the mountains is seen to be
traversed by a number of shallow winding valleys, trending towards
Agrippa, and separated by low rounded hills which have all the appearance
of having been moulded by the action of water.
BOSCOVICH.--This is not a very striking telescopic object under any
phase, on account of its broken, irregular, and generally ill-defined
border. It is, however, remarkable as being one of the darkest spots on
the visible surface: in this respect a fit companion to Julius Caesar,
its neighbour on the W. Schmidt shows some ridges within it.
RHAETICUS.--A very interesting formation, about 25 miles in diameter,
situated near the lunar equator, with a border intersected by many
passes. A deep rill-like valley winds round its eastern _glacis_,
commencing on the S. at a small circular enclosure standing at the end of
a spur from the wall; and, after crossing a ridge W. of a bright little
crater on the N. of the formation, apparently joins the most easterly
cleft of the Triesnecker system. A cleft traverses the N. side of the
floor of Rhaeticus, and extends across the plain on the E. as far as the
N. side of Reaumur.
TRIESNECKER.--Apart from being the centre of one of the most remarkable
rill-systems on the moon, this ring-plain, though only about 14 miles in
diameter, is an object especially worthy of examination under every
phase. At sunrise, and for some time afterwards, owing to the superior
altitude of the N.W. section of the wall, a considerable portion of the
border on the N. and N.E. is masked by its shadow, which thus appears to
destroy its continuity. On more than one occasion, friends, to whom I
have shown this object under these conditions, have likened it to a
breached volcanic cone, a comparison which at a later stage is seen to be
very inappropriate. The rampart is terraced within, and exhibits many
spurs and buttresses without, especially on the N.W. The central mountain
is small and not conspicuous. The rill-system is far too complicated to
be intelligibly described in words. It lies on the W. side of the
meridian passing through the formation, and extends from the N. side of
Rhaeticus to the mountain-land lying between Ukert and Hyginus on the N.
Birt likened these rills to "an inverted river system," a comparison
which will commend itself to most observers who have seen them on a good
night, for in many instances they appear to become wider and deeper as
they approach higher ground. Published maps are all more or less
defective in their representations of them, especially as regards that
portion of the system lying N. of Triesnecker.
HYGINUS.--A deep depression, rather less than 4 miles across, with a low
rim of varying altitude, having a crater on its N. edge. This formation
is remarkable for the great cleft which traverses it, discovered by
Schroter in 1788. The coarser parts of this object are easily visible in
small telescopes, and may be glimpsed under suitable conditions with a 2
inch achromatic. Commencing a little W. of a small crater N. of Agrippa,
it crosses, as a very delicate object, a plain abounding in low ridges
and shallow valleys, and runs nearly parallel to the eastern extension of
the Ariadaeus rill. As it approaches Hyginus it becomes gradually
coarser, and exhibits many expansions and contractions, the former in
many cases evidently representing craters. When the phase is favourable,
it can be followed across the floor of Hyginus, and I have frequently
seen the banks with which it appears to be bounded (at any rate within
the formation), standing out as fine bright parallel lines amid the
shadow. On reaching the E. wall, it turns somewhat more to the N.,
becomes still coarser and more irregular in breadth, and ultimately
expands into a wide valley on the N.E. It is connected with the Ariadaeus
cleft by a branch which leaves the latter at an acute angle on the plain
E. of Silberschlag, and joins it about midway between its origin N. of
Agrippa and Hyginus. It is also probably joined to the Triesnecker system
by one or more branches E. of Hyginus.
On May 27, 1877, Dr. Hermann Klein of Cologne discovered, with a 5 1/2
inch Plosel dialyte telescope, a dark apparent depression without a rim
in the Mare Vaporum, a few miles N.W. of Hyginus, which, from twelve
years' acquaintance with the region, he was certain had not been visible
during that period. On the announcement of this discovery in the
_Wochenschrift fur Astronomie_ in March of the following year, the
existence of the object described by Dr. Klein was confirmed, and it was
sedulously scrutinised under various solar altitudes. To most observers
it appeared as an ill-defined object with a somewhat nebulous border,
standing on an irregularly-shaped dusky area, with two or more small dark
craters and many low ridges in its vicinity. A little E. of it stands a
curious spiral mountain called the Schneckenberg. The question as to
whether Hyginus N. (as the dusky spot is called) is a new object or not,
cannot be definitely determined, as, in spite of a strong case in favour
of it being so, there remains a residuum of doubt and uncertainty that
can never be entirely cleared away. After weighing, however, all that can
be said "for and against," the hypothesis of change seems to be the most
probable.
UKERT.--This bright crater, 14 miles in diameter, situated in the region
N.E. of Triesnecker, is surrounded by a very complicated arrangement of
mountains; and on the N. and W. is flanked by other enclosures. It has a
distinct central mountain. Its most noteworthy feature is the great
valley, more than 80 miles long, which extends from N.E. to S.W. on the
E. side of it. This gorge is at least six miles in breadth, of great
depth, and is only comparable in magnitude with the well-known valley
which cuts through the Alps, W. of Plato. A delicate cleft, not very
clearly traceable as a whole, begins near its N. end, and terminates amid
the ramifications of the Apennines S. of Marco Polo.
TAQUET.--A conspicuous little crater on the S. border of the Mare
Serenitatis at the foot of the Haemus Mountains. A branch of the great
Serpentine ridge, which traverses the W. side of this plain and other
lesser elevations, runs towards it.
MENELAUS.--A conspicuously bright regular ring-plain, about 20 miles in
diameter, situated on the S. coast-line of the Mare Serenitatis, and
closely associated with the Haemus range. It has a brilliant central
mountain, but no visible detail on the walls. On the edge of the Mare,
S.W. of it, there is a curious square formation. The bright streak
traversing the Mare from N. to S., which is so prominently displayed in
old maps of the moon, passes through this formation.
SULPICIUS GALLUS.--Another brilliant object on the south edge of the Mare
Serenitatis, some distance E. of the last. It is a deep circular crater
about 8 miles in diameter, rising to a considerable height above the
surface. Its shadow under a low morning sun is prominently jagged. On the
E. are two bright mounds, and S. of that which is nearer the border of
the Mare, commences a cleft which, following the curvature of the coast-
line, terminates at a point in W. long. 9 deg. This object varies
considerably in width and depth. Another shorter and coarser cleft runs
S. of this across an irregularly shaped bay or inflexion in the border of
the Mare.
MANILIUS.--This, one of the most brilliant objects in the first quadrant,
is about 25 miles in diameter, with walls nearly 8000 feet above the
floor, which includes a bright central mountain. The inner slope of the
border on the E. is much terraced and contains some depressions. There is
a small isolated bright mountain 2000 feet high on the Mare Vaporum, some
distance to the E.
BESSEL.--A bright circular crater, 14 miles in diameter, on the S. half
of the Mare Serenitatis, and the largest object of its class thereon. Its
floor is depressed some 2000 feet below the surrounding surface, while
the walls, rising nearly 1600 feet above the plain, have peaks both on
the N. and S. about 200 feet higher. The shadows of these features, noted
by Schroter in 1797, and by many subsequent observers, are very
noteworthy. I have seen the shadow of a third peak about midway between
the two. One may faintly imagine the magnificent prospect of the coast-
line of the Mare with the Haemus range, which would be obtained were it
possible to stand on the summit of one of these elevations. It is
doubtful whether Bessel has a central mountain. Neither Madler nor
Schmidt have seen one, though Webb noted a peak on two occasions. I fail
to see anything within the crater. The bright streak crossing the Mare
from N. to S. passes through Bessel.
LINNE.--A formation on the E. side of the Mare Serenitatis, described by
Lohrmann and Madler as a deep crater, but which in 1866 was found by
Schmidt to have lost all the appearance of one. The announcement of this
apparent change led to a critical examination of the object by most of
the leading observers, and to a controversy which, if it had no other
result, tended to awaken an interest in selenography that has been
maintained ever since. According to Madler, the crater was more than 6
miles in diameter in his time, and very conspicuous under a low sun, a
description to which it certainly did not answer in 1867 or at any
subsequent epoch. It is anything but an easy object to see well, as there
is a want of definiteness about it under the best conditions, though the
minute crater, the low ridges, and the nebulous whiteness described by
Schmidt and noted by Webb and others, are traceable at the proper phase.
As in the case of Hyginus N, there are still many sceptics as regards
actual change, despite the records of Lohrmann and Madler; but the
evidence in favour of it seems to preponderate.
CONON.--A bright little crater, 11 miles in diameter, situated among the
intricacies of the Apennines, S. of Mount Bradley. It has a central hill,
which is not a difficult object.
ARATUS.--One of the most brilliant objects on the visible surface of the
moon, a crater 7 miles in diameter, S. of Mount Hadley, surrounded by the
lofty mountain arms and towering heights of the Apennines. A peak close
by on the N. is more than 10,000 feet, and another farther removed
towards the N.W. is over 14,000 feet in altitude.
AUTOLYCUS.--A ring-plain 23 miles in diameter, deviating considerably
from circularity, W. of Archimedes, on the Mare Imbrium, or rather on
that part of it termed the Palus Putredinis. Its floor, which contains an
inconspicuous central mountain, is depressed some 4000 feet below the
surrounding country. With a power of 150 on a 4 5/8 achromatic, Dr.
Sheldon of Macclesfield has seen two shallow crateriform depressions in
the interior, one nearly central, and the other about midway between it
and the N. wall. The wall is terraced within, and has a crater just below
its crest on the W., which, when the opposite border is on the morning
terminator, is seen as a distinct notch. Autolycus is the centre of a
minor ray-system.
ARISTILLUS.--A larger and much more elaborate ring-plain, 34 miles in
diameter, N. of Autolycus. Its complex wall, with its terraces within,
and its buttresses, radiating spurs, and gullies without, forms a grand
telescopic object under a low sun on a good night. It rises on the east
11,000 feet above the Mare, and is about 2000 feet lower on the W., while
the interior is depressed some 3000 feet. Its massive central mountain,
surmounted by many peaks, occupies a considerable area on the floor, and
exhibits a digitated outline at the base. On the S. and W. a number of
deep valleys radiate from the foot of the border, some of them extending
nearly as far as Autolycus. Shallower but more numerous and regular
features of the same class radiate towards the N.E. from the foot of the
opposite wall. On the N.W. are several curved ridges, all trending
towards Theaetetus. On the S.E. the surface is trenched by a number of
crossed gullies, well seen when the E. wall is on the morning terminator.
Just beyond the N. _glacis_ is a large irregular dusky enclosure with a
central mound, and another smaller low ring adjoining it on the S.E. The
visibility of these objects is very ephemeral, as they disappear soon
after sunrise. Aristillus is also the centre of a bright ray system.
THEAETETUS.--A conspicuous ring-plain, about 16 miles in diameter, in the
Palus Nebularum, N.W. of Aristillus. It is remarkable for its great
depth, the floor sinking nearly 5000 feet below the surface. Its walls,
7000 feet high on the W., are devoid of detail. The _glacis_ on the S.W.
has a gentle slope, and extends for a great distance before it runs down
to the level of the plain. Not far from the foot of the wall on the N. is
a row of seven or eight bright little hills, near the eastern side of
which originates a distinct cleft that crosses the Palus in a N.W.
direction, and terminates among mountains between Cassini and Calippus. I
have seen this object easily with a 4 inch achromatic.
CALIPPUS.--A bright ring-plain 17 miles in diameter, situated in the
midst of the intricate Caucasus Mountain range. On the E. is a brilliant
peak rising more than 13,000 feet above the Palus Nebularum, and nearer
the border, on the N.E., is a second, more than 500 feet higher, with
many others nearly as lofty in the vicinity. Calippus has not apparently
a central peak or any other features on the floor.
CASSINI.--This remarkable ring-plain, about 36 miles in diameter, is very
similar in character to Posidonius. It has a very narrow wall, nowhere
more than 4000 feet in height, and falling on the E. to 1500 feet. Though
a prominent and beautiful object under a low sun, its attenuated border
and the tone of the floor, which scarcely differs from that of the
surrounding surface, render it difficult to trace under a high angle of
illumination, and perhaps accounts for the fact that it escaped the
notice of Hevel and Riccioli; though it is certainly strange that a
formation which is thrown into such strong relief at sunrise and sunset
should have been overlooked, while others hardly more prominent at these
times have been drawn and described. The outline of Cassini is clearly
polygonal, being made up of several rectilineal sections. The interior,
nearly at the same level as the outside country, includes a large bright
ring-plain, A, 9 miles in diameter and 2600 feet in depth, which has a
good-sized crater on the S. edge of a great bank which extends from the
S.W. side of this ring-plain to the wall. On the E. side of the floor,
close to the inner foot of the border, is a bright deep crater about two-
thirds of the diameter of A, and between it and the latter Brenner has
seen three small hills. The outer slope of Cassini includes much detail.
On the S.W. is a row of shallow depressions just below the crest of the
wall, and near the foot of the slope is a large circular shallow
depression associated with a valley which runs partly round it. The shape
of the _glacis_ on the W. is especially noteworthy, the S.W. and N.W.
sides meeting at a slightly acute angle at a point 10 or 12 miles W. of
the summit of the ring. On the outer E. slope is a curious elongated
depression, and on the N. slope two large dusky rings, well shown by
Schmidt, but omitted in other maps. Most of these details are well within
the scope of moderate apertures. Perhaps the most striking view of
Cassini and its surroundings is obtained when the morning terminator is
on the central meridian.
ALEXANDER.--A large irregularly shaped plain, at least 60 miles in
longest diameter, enclosed by the Caucasus Mountains. On the S.W. and
N.W. the border is lineal. It has a dark level floor on which there is a
great number of low hills.
EUDOXUS.--A bright deep ring-plain, about 40 miles in diameter, in the
hilly region between the Mare Serenitatis and the Mare Frigoris, with a
border much broken by passes, and deviating considerably from
circularity. Its massive walls, rising more than 11,000 feet above the
floor on the W., and about 10,000 feet on the opposite side, are
prominently terraced, and include crater-rows in the intervening valleys,
while their outer slopes present a complicated system of spurs and
buttresses. There is a bright crater on the N. _glacis_, and some
distance beyond the wall on the N.W. is a small ring-plain, and on the
S.E. another, with a conspicuous crater between it and the wall. Neison
draws attention to an area of about 1400 square miles on the N.E. which
is covered with a great multitude of low hills. E. of Eudoxus are two
short crossed clefts, and on the N. a long cleft of considerable delicacy
running from N.E. to S.W. It was in connection with this formation that
Trouvelot, on February 20, 1877, when the terminator passed through
Aristillus and Alphonsus, saw a very narrow thread of light crossing the
S. part of the interior and extending from border to border. He noted
also similar appearances elsewhere, and termed them _Murs enigmatiques_.
ARISTOTELES.--A magnificent ring-plain, 60 miles in diameter, with a
complex border, surmounted by peaks, rising to nearly 11,000 feet above
the floor, one of which on the W., pertaining to a terrace, stands out as
a brilliant spot in the midst of shadow when the interior is filled with
shadow. The formation presents its most striking aspect at sunrise, when
the shadow of the W. wall just covers the floor, and the brilliant inner
slope of the E. wall with the little crater on its crest is fully
illuminated. At this phase the details of the terraces are seen to the
best advantage. The arrangement of the parallel ridges and rows of hills
on the N.E. and S.W. is likewise better seen at this time than under an
evening sun. A bright and deep ring-plain, about 10 miles in diameter,
with a distinct central mountain, is connected with the W. wall.
EGEDE.--A lozenge-shaped formation, about 18 miles from corner to corner,
bounded by walls scarcely more than 400 feet in height. It is
consequently only traceable under very oblique illumination.
THE GREAT ALPINE VALLEY.--A great wedge-shaped depression, cutting
through the Alps W. of Plato, from W.N.W. to E.S.E. It is more than 80
miles in length, and varies in breadth from 6 miles on the S. to less
than 4 miles on the N., where it approaches the S. border of the Mare
Frigoris. For a greater part of its extent it is bounded on the S.W. side
by a precipitous linear cliff, which, under a low evening sun, is seen to
be fringed by a row of bright little hills. These are traceable up to one
of the great mountain masses of the Alps, forming the S.W. side of the
great oval-shaped expansion of the valley, whose shape has been
appropriately compared to that of a Florence oil-flask, and which Webb
terms "a grand amphitheatre." On the opposite or N.E. side, the boundary
of the valley is less regular, following a more or less undulating line
up to a point opposite, and a little N. of, the great mountain mass,
where it abuts on a shallow _quasi_ enclosure with lofty walls, which,
projecting westwards, considerably diminish the width of the valley.
South of this lies another curved mountain ring, which still farther
narrows it. This curtailment in width represents the neck of the flask,
and is apparently about 16 or 17 miles in length, and from 3 to 4 miles
in breadth, forming a gorge, bordered on the W. by nearly vertical
cliffs, towering thousands of feet above the bottom of the valley; and on
the E. by many peaked mountains of still greater altitude. At the
entrance to the "amphitheatre," the actual distance between the colossal
rocks which flank the defile is certainly not much more than 2 miles.
From this standpoint the view across the level interior of the elliptical
plain would be of extraordinary magnificence. Towards the S., but more
than 12 miles distant, the outlook of an observer would be limited by
some of the loftiest peaks of the Alps, whose flanks form the boundary of
the enclosure, through which, however, by at least three narrow passes he
might perchance get a glimpse of the Mare Imbrium beyond. The broadest of
these aligns with the axis of the valley. It is hardly more than a mile
wide at its commencement on the S. border of the "amphitheatre," but
expands rapidly into a trumpet-shaped gorge, flanked on either side by
the towering heights of the Alps as it opens out on to the Mare. The
bottom, both of the "amphitheatre" and of the long wedge-shaped valley,
appears to be perfectly level, and, as regards the central portion of the
latter, without visible detail. Under morning illumination I have,
however, frequently seen something resembling a ridge partially crossing
"the neck," and, near sunset, a tongue of rock jutting out from the E.
flank of the constriction, and extending nearly from side to side. At the
base of the cliff bordering the valley on the S.W., five or six little
circular pits have been noted, some of which appear to have rims. They
were seen very perfectly with powers of 350 and 400 on an 8 1/2 inch
Calver reflector at 8 h. on January 25, 1885, and have been observed, but
less perfectly, on subsequent occasions. The most northerly is about 10
miles from the N.W. end of the formation, and the rest occur at nearly
regular intervals between it and "the neck." In the neighbourhood of the
valley, on either side, there are several bright craters. Three stand
near the N.E. edge, and one of considerable size near the N.W. end on the
opposite side. A winding cleft crosses the valley about midway, which,
strange to say, is not shown in the maps, though it may be seen in a 4
inch achromatic. It originates apparently at a bright triangular mountain
on the plain S.W. of the valley, and, after crossing the latter somewhat
obliquely, is lost amid the mountains on the opposite side. That portion
of it on the bottom of the valley is easily traceable under a high light
as a white line. The region N. of the Alps on the S.W. side of the valley
presents many details worthy of examination. Among them, parallel rows of
little hills, all extending from N.W. to S.E. There is also a number of
still smaller objects of the same type on the E. side. The great Alpine
valley, though first described by Schroter, is said to have been
discovered on September 22, 1727, by Bianchini, but it is very unlikely
that an object which is so prominent when near the terminator was not
often remarked before this.
ARCHYTAS.--A bright ring-plain, 21 miles in diameter, on the edge of the
Mare Frigoris, due N. of the Alpine Valley, with regular walls rising
about 5000 feet above the interior on the N.W., and about 4000 feet on
the opposite side. It has a very bright central mountain. Several spurs
radiate from the wall on the S., and a wide valley, flanked by lofty
heights, forming the S.W. boundary of W.C. Bond, originates on the N
side. There is also a crater-rill running towards the N.W. On the Mare,
S.W. of Archytas, is a somewhat smaller ring-plain, Archytas A (called by
Schmidt, PROTAGORAS), with lofty walls and a central hill.
CHRISTIAN MAYER.--A prominent rhomboidal-shaped ring-plain, 18 miles in
diameter, associated on every side, except the N., with a number of
irregular inconspicuous enclosures. It has a central peak. Madler
discovered two delicate short clefts, both running from N.W. to S.E., one
on the W. and the other on the E. of this formation.
W.C. BOND.--A great enclosed plain of rhomboidal shape on the N. of
Archytas, the bright ring-plain Timaeus standing near its E. corner, and
another conspicuous but much smaller enclosure with a smaller crater W.
of it on the floor at the opposite angle. The interior, which is covered
with rows of hillocks, is very noteworthy at sunrise.
BARROW.--There are few more striking or beautiful objects at sunrise than
this, mainly because of the peculiar shape of its brilliant border and
the remarkable shadows of the lofty peaks on its western wall. There is a
notable narrow gap in the rampart on the W., which appears to extend to
the level of the floor. The walls, especially on the S., are very
irregular, and include two large deep craters and some minor depressions.
If the formation is observed when its E. wall is on the morning
terminator, a fine view is obtained of the remarkable crater-row which
winds round the N. side of Goldschmidt. Barrow is about 40 miles in
diameter. According to Schmidt, there is one crater in the interior, a
little S.E. of the centre.
SCORESBY.--A much fore-shortened deep ring-plain, 36 miles in diameter,
between Barrow and the limb. It has a central mountain with two peaks,
which are very difficult to detect.
CHALLIS.--A ring-plain adjoining Scoresby on the N.E. It is of about the
same size and shape.
MAIN.--A very similar formation, on the N. of the last, much too near the
limb to be well observed.