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

I-tURE OF TH'r,: lEARtH:'s OlRIIT. 85
angles to the ccli}tic, in whl]ich case, the pole)s of tle earth
wotuld ave l)een situlatted in the ccliptic itself; then in l ifferent parts of the earth the appcarancest would have bleen as
folows........:- o a spectator on the equator, the sun81,as he left the
vernal cquinox would( every day pclform htlis diurnal revolutioln
in a small er and smaller circle, until hli reached the north pole,
when he would halt for' a moment andt then wheel about,land
return to tlhe equator in tle reverse or(ler. 1The progr-ess of
tle sun t-hrough the southern signs, to tile south} pole, would
be similar to that already described. Such Nwoutld be the appearances to an inhabitant of tlhe equatorial regions.'.To a
spectator livingt it anl oblique spherll' in our own latitudt for
example, the sun, while north of tie equator, would advance
continual-ly nortlhlward, makiing his diurnal circuits in parnllels
fllrther and furtler distant friom tle equatorI, until hel reached
the, circle of perpletal apparlition, after -whichl le would climb
lby a spiral course to the north start and then as rapidly return
to the equator.:By a similnar pro gress southward, the sun
would at lengthl pass the circle of perpetu'al occultation, and
for some tilme (whicl would be longer or slorter, according to
the latitude of the place of observation) there would be contitnual night.
The'great vicissitudes of Iheat and cold which would attend
suchll a motion of tle sun, would be wholly incompatible witth
the existence of either the animal or tle lvegetable kingdolmns,
and all terrestrial nature would be dloolmed( to plerl)etual sterilit)y and desolation. lThe happy provision \which the Creator
]las 11made against such extremzevicissitudes, by confining the
changes of the seasons Nwitlin suich narrow bounds, onspil'es
withl many othet express arrangements in the economy of
nature to secure the safety and comfort of the human race.
FIGURE. OF T1tl'' FART t:Xl0t1t'S IORBIT.
1 62. Thus far we have taken the earth's orbit afs a great
cirele, such beingt tllhe projeetiol of it on tlhe celestial splhere.;
but we now proceed to investigate its actual figure.
Were the earthl's path a circle, having the sun in tlhe center,
the sunl would always be at the same distance from us; thait is,
the.radius vector (the name given to a line drawn from the