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

1:82 tHEl,: LhAN Ers.'lhuls Vrenus, while going fro'm 13 tllrough ]) to A (Fig. 61),
nloves ill thle orlder of tile signs, or from west to east, and
would appear to traverse the celestial vault B' 8' A' fi'rom right
to left; but in p)assing froil A_ through C to B1, her course
woluld 1)e retrograde, returning oil tile same are friol e le(ft; to
right..I tlte eartll v/ee at(, re'Cst, therefore (and thle sun, of
course0, at rest), tlhe inferior planets would appear to oscillate
back\ward and forward across thlte sun. lut it iusnnt be recolleeted that the earth is movingl in the;tsame direction wvith the
planet, as respects tlhe signls but with a slower motioln.'tis:modifies the apparent motions of thie planet, accelerating it inl
the superior, and retardling it in the inferior conjunctions.l
Th'us, in figure 61, Venus, wllile moving through B.l).\, would
Fig. 61.
seem to move iln the heavens froml' to A', were the earth at
rest; butt meanwhile the earthl chang;es its position fr'om i', to
E]', by which means tlhe planct is not seen at A', butt at A",
being, accelerated by the are A'A", in consequence of flte
earth';s motion. Onl the otller hand, whell tlhe p1laet, is p:assing tihrooulgh its inferiol colljlunetion AtOl, it woultl lappear to
move Iback\lward ill the heavens A' to 1B', if the eartll were at
rest, 1but fiom A.' to 113", if the carth has, in the mleal time,
movedl from E to E', being retarded by the arc B3'B1". A\lthough the motions of the cartlh have the effect to accelerate