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

LUNAR GEOGRAPHY.'T 15
205:. The appearantlces described in the'tlre(toin a1 rtlicles
are obvious ly dutle to (diflerenletes of elevatiml, silnce tltey are icTealedt by the sun-lighlt fidling on11 thlem att conlsidetablt oliquity. 1ltcy comet into view in successionl as tlhet sunt riscs
uponl them, during the first two quarters, or t St and lct ave s
thel in shiade in tlhe last two. At tlhe fitll moon, the stti
rys 1and our line of tvision coinlcidle inl directiollt at11nd no s dows aippear, and thle fatures of mountain and valley are ontly
inpert'ctlyx seenl. ]ltnt a peculitarity of anotlher kiltld 1lresents
itself at the time of full lloolt. lTherf e hnlitninloust stripjes cxtendinr; fitrom several of tlie rintg-mlountains ill fittaiglt litecs to
the di.taatnc of hn}ludreds of mtilcs.'1}thcy are not ridges, siI(ce
they east no sladows Ias thle terminator )asses tlhetn; and tlte
difflencllce of illullination llmTust result; from i (1,l ifference of rellectivce power. ulnt l)erlItPs nto satisfiactory re ason can ibe givett
for th}eir rem tarka)ble arrangement. I ttcy are somcti tns tclt'nd
[la(te(a sitlt.'[H+ e most extensive systcslll of thiis kind occur
aroutl d ~TClol, C(otpernicus, 1Kepler, a tnd A nax'agorass.
Tlherle is no atCppettarance of fluidity on the ltnar surthce, ntor
anyt sucl conltition as wte mighllt exl)et to result f'i omn tlhe flow
of a liquid. Alt inequatlities are algular anld rigid, itnstead of
beinglt softened doswnl lby the action of w-xater.'Ithere ar10e nlo
chnitgtens \wielt w ic ight be ascribed too tim growth a\td decay of
vgeet atiotl. INo spot is ever colccalcde by a cloud, or1 ditnted
by an impl re, tatmospllere. Thle cold is problably too inttcense
fir the existence of a liquiid substai ce, jutst its thte eartit Nwould
be) if it vwere destltiute of an atmospltere, and tflhus exposed to
the low temperlat ure of the space tlhrotllghl whicll it tcravels.'
206. T'e ethod c(/ q tifietmabi;n the i h;/ ht eg1 b' lunar,nmo.tn(miis is ( drlloms;
Let Ae () (,Fig. 45) be tlte illlminated hemisi lere of tflhe
m1oon1, SO) a solar ray touchic r tlhe mt oon in 0, a )point in tlim
circle whiclt s-eparattes thle emlig}hteclle-d from theI dark ptlt of
the moon. All tlic part O l)A will 1be in diarkness; lt)t if this
parti contains a mountain lti? so elevated tttat its sumnt it M.;reaches to thel solt~ latt r 8y()5~t tl c point MI will be elliglttencd..
For1 a fuller dcescription of the mtroonl's stsrfitce, see Itarllnertt'' 1i[and-book on
Meteorology aond Astro)nomy,t p)p. 205 —212.