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

INYeRIOOlR rLIANl'i.f...ftOUliY AN) V,E US. [t 81
or when it has the same longitude. hlcrein'y and Vcnuis have
eachl two conjunctions, the inferior and tihe superior. The
inzfer-ior comjl Ectzio is its position when inl colnjunlltionl onl the
same side of tlle sun w\ith thi earth, as at Q ill the figur; the.p)eriowr co'azunetiown is its position when onl the side of the Sulll
most distant from tile carlth) as at 1.t
304. The period occuplied by a plancet between successive
colnjunctionls of the samle ]kiund is calleld its Sylaodical'tevolution.
BHoth the planet and the carth bleing in motion1, the time of the
synodical revolution excceds that of the sidereal revolution of
Mercury or ncllmus; for when the planlt conics round to the
place lwhere it before overtook the earth, it does not filnd the
carth at that point,!umt far in advance of it. Thus, let MerC1cury collo illto its inferior colnjunction at Q (Figs. 60). It
a)bout 88 (days the planet will come round to the same p1oiInt
again; but Imeanllwhile tlhe earth has moved forward tlroutglt
nearly a fourth part of her revolution, and wvil contiinue to
move onwardl wllile M:Cercury, witll a swifter motion is twollowing on to overtake her, the case being analogous to the hlour
and millitc handl of a clock.'lLaving the site-ldead l period of a
planlet, wlichl Ilmay always 1)c accurately detrmintc d by observationl, we may ascertain its synodical period, s tfollows:
ily the ttable in article 301, the mean daily motion of eNIOr —
cury is 4: 5' 32".G t1Y732".6, and that of the eartlt is 59'
3:8 ".3. T hc8cri>rc, J:L,:,S.6. 3........ 35. 8.3 - l.1.18 ".3, whllich
is the aver\'age gain of Mlercury over tehe eartht in a day. But
itl order to overtake the carth, er'clry must complete one
revolution zand ars much of another as the earth has )performed,
until thte 1)lanct overtakes it; thrat is, the planlt must atin an
entire revotlltion. Now,
1118:1".3: 1 day:360~ 11.:.8 days, the syndodwical)eriowd oCJC![arcy. hIn like 11mane1r, the daily gain of Venus is,2219".5,
and
2211.9".5: 1l day: 360~ 583.9 days, the synolicdal. periolo of
305.:17we ot'ioit of a(tn kferi7or'.)iaet iS direct in insslity
through, its sulmerior conjwtc tion, rnid r'eetbograale in pa18ssing
1/tiro1tth its i Of'inf or eo jzunetioam.