An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

1114'.Iil 10 I t.M OON.
others are level..li'e l)'oketi 1'regions al)pear briglhtier t all ti}l
smlootl tracts. Tlhe latter were formtcrlyt takenl ftor seas, andl
rece(ivedl nalns accordingly.; as A (I'i. *, Ftr.), matre /tounor..tnte;
BJ, macbs? n tb.btati,, &c. But it)provedl telescopetts h}ave sltew
thatt thley are extenlsive )lailns, hlavting' inequallitiets wihlicth,
thlolgltl compllarattivcly low, ar e irmtanlent. Thaltt: tllere are,floiitwa',f is is known l l)y the followt\ing ildicattiolls..I\ tile ter1illrat. tc avattces over the disk, ttCe ligllt strikes tl:he hglllest;
petak,'wlt]iclh appear a brigtts P oints t little way upon th:e (la rk
Plart of tthe nltoll. A fter the terln llt r has passed oever themt,
they )r'jeet sihadows away f'roi ftle sun, corresponwling to the
appart' it shalpe of the 111ountl taitt il d l rowi ill S 1'Ett, as the
rays fiatl l1 moe nearly vertical. And alain, i the waning of
the mltoontll thlte sadft(ows are east inl the opposite direction, lengtheting luntil t:he dark part oft the disk reachtes tthem, antd the
summitts once morle become isollatedl brig'ltt points, and thten (iuslapp, ear. A vicw with a good telescopte, continuled fotr fiteen
minlluttes, xvill often show )rcpt tlible chltanltges inM thlle position of
tle sladows, antid the shtape of illuminatctd pteaks.
20x4. T heva/l/.s very genferally hI ave a circular fIrl-n:, varyin"t in (liatncel-:er friol I mile or two ui)p to sixty mliles; tihe
Ilioituiltai. ridgeo, Nwhic] slturrot ds them), being of a ri lg foirm,
uCse.ally mttuch in ore prci(pitous oil the, inner side thlan tlhe
oulter.'r.itc! hcigqhts sunl3t rounlldigl thelISei \valleys fare cattlled'iq-.itfifti'fti,. (.)ne olr l torci- conical mounlllt ains frequently occuipy the center of thle as.ea intclosed withil tle ring. Some of
the plrti ip al re, Nc. 1..7 qIc/r o; 3. %O: ri'iat. s;
4../'.Atrf f'rc/t,s' &c. (1ig. I., t.14 ) Thiere are r alsoo ttl'ar1e' a llad
less rcgular areas, surlou(ltt ed ly lountails, called blt.t ewa
7-la:in.sr. The dliamit ter of soine is:130 miles; anld tlley giterll Itte smallll molluntains, botl of thef t conical andt l oing 1'tll n
scattered over th e l plaiin. "The largcs t aire (',lavi-s, 1'5' ( o,
IRc ioinmota, PIb t /w/i,.Ala, pine, Iosna.fl'o iwus. Bes(ides the
( peculik. foln' s mow nenitioneld, thlere are chaiwls and spulrs of
lloulttailts, reseCtlubling terrestrial rantges.'
r''ihte htlnr map of tleer a11d Madtler, 2A feet in diameter, contains a very perfeet delinteation of tihe mountait \and valle'ys of thle moon, accolpainied by their
ltMleS.