Astronomy. AAS 
The opinion has been often expressed that the asteroids are the 
fragments of a large body which once existed between Mars and Jupiter. 
This opinion has lost none of its plausibility by the discovery of Astrea. 
Indeed in the position of its node, in its period and eccentricity, this 
planet conforms very nearly to the mean of the elements of the four 
former planets. It was remarked by Dr. Olbers that according to the 
above hypothesis, since the orbits must all have diverged from the same 
point, so they must have two common points of reunion in opposite parts 
of the heavens. ‘The following diagram will show how nearly this con- 
clusion conforms to observation. 
This diagram represents a por- 
tion of the orbits of the asteroids 
as seen from the sun, correspond- 
ing to a heliocentric longitude of 
180° to 195°, and the circle which 
is added has a radius of four de- 
grees. We perceive then that a 
circle of four degrees radius em- 
braces at least five degrees of the 
orbit of each of the Asteroids, 1s007 185° 180° 195° 
Astrea included. We see also 
that if this small circle had been faithfully watched for four years, these 
five planets must all have been discovered. This is precisely what 
Olbers undertook to do, and his search was rewarded by the discovery of 
Vesta. With such perseverance did he maintain the watch, that he an- 
nounced that no new planet could have passed between 1808 and 1816. 
In this he was certainly mistaken; Astrea glided by him unperceived. 
In may be thought that the above theory requires that the orbits 
should all pass, not almost, but exactly through the same point. The 
answer to this objection is, that the orbits are disturbed by the attraction 
of the other planets, and that we may readily admit that atno very dis- 
tant period, the orbits did all pass through a common oint. 
t may be interesting to compare the dates of all those planets, the 
period of whose discovery is known. They are as follows :— 
Uranus, March 13, 1781, by Herschel. 
Ceres, én. I Ten, Piazzi. 
Pallas, March 28, 1802, Olbers. 
Juno, ept. 1, 1804, Harding 
Vesta, March 29, 1807, Olbers 
rea Dec 8, Hencke 
This last discovery may perhaps excite astronomers to set a new 
watch, to intercept any other planets which may presume to venture upon 
this field of a former catastrophe. 
Sxeconp Sxnizs, Vol. I, No. 3.—May, 1846. 57 
