MOTIONS OF THE PLANETS.
27
Names
of
the Planets.
Distances fromthe Sun inMiles.
Diameters
in
Miles.
Revolutions in Orbits.
Rotation roundtheir ownAxis.
Vesta.
Juno.
Ceres.
Pallas......
37,000,000
69,000,000
95,000,000
145,000,000
225,000,000
254,000,000
263,000,000
263,000,000
495,000,000
907,000,000
1800,000,000
3,224
8,648
7,912
4,431
unknown
1,400
170
unknown
90,000
79,000
35,000
Years. Days. Hours.
» 88 „
„ 224 17
1 »> it
1 322
3 274
4 128
4 200 „
4 200
11 315
29§ „ „
84 ,, „
Hours.
24
23§
nearly 24
24§
unknownunknownunknownunknownnearly 10
10*
unknown
Before we quit this rapid view of the planetary system, it will be necessaryto make a little extension of the general terms, in which, for simplicity ofdescription, its forms of arrangement, dimensions, and movements, havehitherto been spoken of.
For conciseness we have hitherto -spoken of the planets as moving in circularorbits, and described the planets themselves as being of a spherical form. As weadvance, however, it is necessary gradually to extend our views on these points.It must now be understood that the planetary orbits are, in strictness, ellipses ;not, it is true, differing greatly from circles, but still they are decidedly of anelliptical form. In like manner it should now be explained, that the figureof each planet is not, in strictness, spherical, but is, in every instance, more orless spheroidal, as that of the earth ; a diameter, measured from pole to pole,being somewhat less than a diameter measured through the equator. Thesedifferences will be accurately stated, as we successively examine the detail ofeach planet.
It must also be clearly understood, that all the planets, as well as the sunitself, rotate in a direction from west to east, on axes that remain nearly parallelto themselves in every part of their orbit, and with velocities, respectively, thatare sensibly uniform. As the planets rotate on their axes in a direction fromwest to east, so they also perform their respective revolutions about the sun,in the same direction; and, further, as the primary planets themselves moveround the sun from west to east, so do the satellites of each move round theirrespective primaries in the same direction.
The portions of time spoken of, with reference to the movements of theearth and planets, must be understood to be all derived from some undeviatingphenomenon in nature, to which we can at all times refer for proof, if necessary,of an accurate reckoning: as, for instance, the portion of time we term a year,is established by the earth’s performance of a complete revolution about the