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

300.,xMtf ANI W'JlE.s.
D)ianeter Meanti apparent
in Mitite.. Diailtter. r, Ma, yolmnoe.
M:~ rcury,5,...^.. P950'' "9. 8". 8
V-enusl,...,800.,. 9
Etarth.......,92 100 1
Marns,..... 4,5000 " 15'6
]laneltoid s,.... 0".5 uncertain.
Julpit er.... 89,000 37. 37,171. 1,400
Saturn,..... 9,(00 16". 11.) 12 1,000'
ranus,.... 35,000 4. 1,5t 80s
NeiCl)tune,.. 31,000" 2".5 672 60
])iagtrams and orreries, as usually constructed, whtoly fail of
giving atny just conceptions of tih distancds of the planets
fron tile slun andlfi om each other. If we replresent, for instanc&c, the distance. of the earth by 1 foot, we shall require 30
feet in order to reach the place of.Ncl)tune; and cwhen vwe
lave constructed a diaglral oil so large a scale, w\e lmust still
bearl in mind that each foot represents a space of lnearly 100
mlillions of mniles.'I
We remark herle a great diversity in regard to mag n'itude-
a diversity whlicll does not appear to le siubject to anyi (efinite
law\.'Whil Venus, a inlfrior' planect, is nilne-tenth.ls as largo
as the earth, Mars, a superior pl anet, is oenly oe-sixth, w\lilo
Jupiter is fourtcc l lllludred timlmes as lart'ge. A. lthoitgh several
of trhe planets, wheni nearest to us, appear brilliant1 a11d large
when colmpalred \itl tilhe fixed sta rs, yet the angle which they
subttend is very small, that of Veus, the greal'test of all, neverl
exceedling about V1', or more exactly an."d2, and that of Jlupiter,
when greatest, bilng only about {- of a mlinute.
W Hind.
Jt Fur thle lpurposes of illustraztion to a class or to a loplutlar aulience, the following plan of representation is recommended, not only for thle entire solar system, beut for each of the subordilate systems, as that of Jupiter or Saturnl,
Stretch upon the wall a piece of black cambric, as long as the room will allow,
saw 30 ft. Thi's length ay bo taken for the radiis of Ncptmne's orbit. At ono
tlend, attach a circlet of white cloth,. itch i tn diameter for tfhe suti. From it as
a center describe arecs across the cloth at proper distances for tite several orbits,
aitl sew\ white tape on these arlcs. We thenl have tihe l)lanetary di-stances, and
thet size (,f thte sun, upon one scale. lthe planets themselves can not bb re)preented(, sintce the tlargest of them would be almost invisibly small.'the cloth
may be convenienwtly rolled up, when not inl us.