D. Kirkwood on Certain Analogies in the Solar System. 215 
3. The period, (1969 days according to Table I.) which my 
analogy assigns to the asteroid-planet, is almost exactly commen- 
surable with that of Jupiter; eleven of the former being about 
equal to five of the latter. 
{ we assume that the period of Encke’s comet has dimin- 
ished uniformly at the present rate, the time of revolution, at no 
very remote epoch, was 1238 days; that is, seven of its periods 
_ Were precisely equal to two of Jupiter’s. 
ae 5. Among the swarms of minute asteroids which may be sup- 
posed to revolve in this zone, there have probably been many 
whose periods were commensurable with that of Jupiter. Those 
completing a revolution in 1444 days—precisely one-third of Ju- 
piter’s period—would be in conjunction with that planet, in the 
same point of the orbit once in every 4332 days. ‘The conse- 
quence in such cage would be a permanent derangement 
6. It is possible that in consequence of mutual attractions, in- 
tersections of orbits, &c., new combinations and aggregations of 
matter not unfrequently occur in this part of the planetary system. 
Important discoveries, I have no doubt, are yet to be made in re- 
gard to those mysterious objects. 
« When my analogy was discovered no asteroid had_been de- 
tected beyond the orbit of Pallas. Since that time, however, 
two of those small bodies, Hygeia and Psyche, have been found 
at distances considerably greater: the orbit of the former being 
exterior to that of the primitive (hypothetical) planet, and that 
of the latter nearly coinciding with it. /mean distances, 
periods, and inclinations of the small planets, together with the 
date of the discovery of each, are as follows: 
‘ » TABLE IL § 
Name. ae Mean dist, | Period. | Inclination. ate of discovery. iscoyerer, 
BRE Oi See eee 3 9018 | 1193d| 5° 53’ |1847, October 18, | Hind 
Gio, SS reac! ees 93349 | 1803 | 8 28 |1850, Sept. 13, nd. 
i sikgn eee 3:3612 1825 4 g  |1807, March 29, Olbers 
OR ge oe 93855 | 1846 | 5 28 |1847, August 13, 
el ets, @|-23862 | 1346 | 5 36 1848, April 26, Graham. 
Hebe,.........7.| .9go49 | 1879 | 14 47 |1847, July J, Heneke. | 
arthenope, gees 24483 | 1899 | 4 87 |1850, May 11, De Gasparis. 
Base ass v0 9-4619. | 1410 | 5 . 36. |1852, April 17, | Luther. 
Astrea, 0.6.5. 25774 | 1511 | 8 19 |1845, December 8) Hencke 
Pree. FE 5. 90-5895 | 1516 | 16 38 |1850, November 2, De Gasparis 
POR eas ad). s 2-584 1518 |. 9 6 41861, May 19, Hind. 
OMIA... 2.4. 96476 | 1574] 11 49 |1801, duly 19, . |DeGaspans 
wee Pelee sien o-6687 |.1592|18 8 Sd seer Sat 
holon ue ee 1681 | 10 87 |1801, January -, 
Wieety ale, parte 1687 | 34 37 |1802, March 28, [Olbers. 
PEP R as 05 ns om 30661 961 | 3 30 |1852, March 17, | De Gasparis. 
ot eee 31514 | 2048 1 3 47 |1849, April 12, | De Gasparis. 
Application to Tranus-— 1 be rotation-period of Uranus has 
hever been determined by observation. With the masses adopt- 
_€din Table L. it is found, according to my analogy, to be about 
