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

.lINAR OGl;(-lGRA'ltY. J1.g'from tlhe taitbles a-uly natural nutliber, except PtM.X the, qualtity
so8011tt. ltTie heiAitl ts f st01110e niuoiiitailis, detetmitied in this
way, have been fi)und between three and four miles.
Whell tile 100moon is exactly at quadrature, Ml S isa 1ig t
atln,g and (bcing coincident iwith (ON") is obtailntcd directly tfrom the micromneturical measurement of tihe atlet E; from
which FMf is dclrived as before.
208. Setbroeter, a ~Germanl astronomer, estimated tile heightts
of thle luntar mountaills by observations on thtcibr saut(/ow. Ito
made t llhte iln some eases os high as of tlhe smti-diatl Cr
of tilhe mloon, thlat. is, bout I5 miles. The1 same astronomer
also estilnates tlte depthls of some of tie lunar valleys at mnoro
th-an tiur m-niles. Tl ente it is inferred that thte moon's surfac
is liorel blrokelt anld irreg1ularlflt'an that of the earth, its loullntains being hligher and its vtlleys (deeper in proportion to the
size of tile nlool thllal those of the earth.
209. FIt has solmetimes lbeen supposed that tlhere are slight
indica,(tio-lns of an atmospliere labout the moon. This is pro'b)ably tan error.'Thie scverest test of a perceptible at lmsp1)tre
w\-ould be thic effclt oni a star, at tihe beginning and end of its
occulltation by thie moon. The star wvould appear to )te tcl'ta'i
etd a little ill its diurnl l motion, just b)efore disappearing', lld
jtust afler realppetrillg, in consequence of thte )belldinlc of thlt
ray s\ wliich} comei f'ron it, as they pass thie edge of the moon's
(disk, andl probably some loss of ligtt, would in that case 1be
perceptible at thle same moments..3ut tile most careful observat.ions hlave failed to show any,such (letention; and as to
lo)s of light, thle star,h oiln coning up to tlle edge of tire 11oon
d(isalapears all at once, wvith a suddennest s which is staltIing.
If theicre is an atmosphere, it calnnot hatve a thousandth part of
tlte delnsity of the cartlt's."
210.,Tihe improbability of our ever identifying art-i/tcial
sl/trettulres' ill tle loon may l)e infcrred from the fact tthat a
line one mlo e mine t lenglth ii tlhe moon slubtends atll anglel at the
eye of only about one second. If, therefore, works of art weroe..... -.-..