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

20t'rtnl}t.xA NT'ES.
soon. And, as the earth departs firom Jupiter, Roo00elrc perccived tlat the eclipses occur later th.an they should do accordiug to the average interval, and that thley are 16m. 2GO.6 too
late), w\tlen at the greatest distance. lIe attributed this effect
to thle pro'gressive motion of light.:)iividlig:19()0,000,000
mil;es, te diaineter of the earth's orbit, by loin6. 56~.6, the
timle of crossing, e follund 192,,600 miles perl second to be the
velocity of light. This seemled, at first, quite incredible, andti
was lreceived -withl distrust. 1 But its correctness was soon Cstablished, by the diseovery of the aberration of tlme stars,
whicl gives the same result.
34 1. SA^'URN coAmes next in the series as we rcccede f'om
the sui, and has, like Jupiter, a system -within itself, on a
scale of great magnificence. Iln size it is, next to Jupiter, the
largest of the planlets, beillg 79,000 miles in diameter, or nearly
I1.0 tinies as large as tll eartht ill diameter, and about 1.000
timnes as larlge ill volume. -It has likewise belts on its surface,
alnd is attended by cieiht satellites. B1ut a still more wonderftul
appenldage is its Jiinly, a broad wlheel encmolllasssing the p1lanct
at a great distance fiom it. W\e have already intimated that
Saturnt's system is oni a grand scale. As, however, Saturn is
distant fiomli us nearly 900,000,000 miles, w\ are unable to obtain the samie clear and striking views of his phenoieltna that
-w\e 1do of the phellnomena of J uplliter, altlougl tlhey really p1)csentt a more wondlerlfill mcchanisml.'lThef disk of Saturn Awas
described by Sir William Hellcsclll as l having the foirm of a
rectai:gle with rounlded corners; but reftied measurlements,
lolre recently made, sltow that it is aln ellipse, and the planoet,
therefore, an ellipsoid. Its equatorial exceeds its polar diam-ieter by labout onte-tentltl.
Tlec bells of Saturn, although clearly discerned by a good
telescope, tare far more indistinct than those of Julpiter. Spots,
whichl occasionally aplpear on the belts, thave enabled astrollomeirs to (etermine thle timle of the diurnal rotation of Saturn,
which is fotund to be about ten hours and a haltlf (-.Obu. 299m.).
342. When viewed with a good telescope, the body of tho
Ifild.