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

15,1'TIii A1OON.
Sux, are ascer'tained very nearly like those of a l1nar cctlipse.'.l'Tl shladow of thle mloon travels over a portion of the earthl, as
thlc sihadiow of a sinalll cloud, seent fi'o ll a teminence in a clear
day, riides along over hbills and plains. ].,ct us imagilne ourselves standing, oil tle moon; thn wve siltall see the earth partially cclipsed 1)by the shadow of the moon, in the samite minter
s we\ now se the loon1 eclipsed by the cartlh's shldow; anll
we might prodccct to fild the lengthll of the shfadow, its lbreadtl
where it. cclipscs t.e carthll the breadth of the penumba, alnd
its duration and (uantity, in tlhe same way as e have ascertainlld these particulat-rs fobr an cclilpse of tlie leooll.
31t, altllougll thle general clharacters of a solar celipse might
be invcstiated oil thltcse principlcs, so far as rcspeets tlhe earth
at large, yet as the appearances of the samle eclipse of tile sutil
are very ditlfernt at (liftrenlt lplaces on the earthl's sulrfac it
is necessary to ealculate its l)culiar aspects for eaclt place separately, a cilrcumstance which makes the calculation of a solar
cclipse much lolre complicated and tedious than of all eclipse
of the O11001n. Thi mo nrl, when l sh enters tlhe slhadow of the
carth1, is deprived of thel lig]ht of the part immersetld, and that
lart appefars black alike to all places where tle moon is above
thle horizon. B3utt it is not so with a solar eclipse.'We do not
sec this b1y thle shadow cast on tile earth, as we s'should (do if
Nwe stood oil tIc moon, but by tlhe interposition of thle 1moo1n
b)etween us a(nd tlle sun; anid lis edge mlay be ]hidlden fi'lom onl
observer whVilCe he is il fuill view of anothler only a few miles
distant. Inl strictness, the pltenomnenon should be calledc an
occultaltion, not an eclipse, of tlhe sunt; tihe euart/ is eclipsed, or
obscured by a shadow east upon it, whtile tlhe sutn, to those
withtin the shadow, is Aidtdee by an intervening body.
263. AVe have compared the motion of the moonl's slhadow
over the surface of the earth to that of a cloud; but its vt;loctdJ
is incomparably greaterl. The mean ll motion of thoe mloon
around te}tc earth is about 33' per hour; but 33' of tIhe moon's
orbit is a80 miles, and the shadow moves of course at tIhe
saime rate, or 2'280 miles per houlr, tx.raversingy the entire disk of
the e(artlh in less thanl four hours. T is is the velocity of tlhe
rtladow whenll it passes pe'rpczdieulatcly over the earth; when
thile dilrectioll of the a(xis of tlhe shadow is oblique to thle earth's