. 165 



The possibility of determining by calculation, even approx- 

 imatively, the epoch of such a cosmical event, which it is sup- 

 posed would be at the same time the epoch of the formation 

 of the small planets, remains more than doubtful, from the 

 complication produced by the already large number of the 

 " fragments" known, the peculiar retrogression of the apsides, 

 and rriotion of the nodes.* Olbers describes the region of the 

 nodes of the orbits of Ceres and Pallas as corresponding to 

 the northern wing of the Virgin and the constellation of the 

 Whale. Certainly Juno was discovered in the latter by 

 Harding, though accidentally, in the construction of a star- 

 catalogue, scarcely two years after*the discovery of Pallas, 

 and even Vesta in the latter, after a long search during five 

 years, conducted upon hypothesis. This is not the place to 

 determine whether these results alone are sufficient to estab- 

 lish the hypothesis. The cometary clouds, in which the small 

 planets were at first supposed to be enveloped, have disap- 

 peared on investigation with more perfect instruments. The 

 considerable changes of light to which they were said to be 

 subject were ascribed by Olbers to their irregular figure as 

 being " fragments of a single destroyed planet."! 



JUPITER. 



The mean distance of Jupiter from the Sun, expressed in 

 fractional parts of the Earth's distance from the central body, 

 amounts to 5 - 202767. The true mean diameter of this plan- 

 et, the largest of all, is 77,176 geographical miles; equal, 

 therefore, to 11 -255 terrestrial diameters, about one fifth great- 

 er Ahan the diameter of the more remote Saturn. His side- 

 real revolution occupies lly. 314d. 20h. 2m. 7s. 



* The flattening of Jupiter, according to the measurements 

 by Arago with the prismatic micrometer (which were intro- 

 duced into the Exposition du Systeme du Monde, p. 38), 

 is as 167 : 177, consequently T |. T , which agrees very closely 

 with the later determination (1839) of Beer and Miidler,J 



* Gauss, Monatl. Corresp., l)d. xxvi., p. 299. 



t Mr. Daniel Kirkwood (of the Pottsville Academy) has ventured 

 upon the undertaking of restoring the exploded primitive planet from 

 the fragmentary remains in the same manner as the animals of the prim- 

 itive Earth. He finds for it a diameter greater than Mars (of more 

 than 4320 geographical miles), and the slowest rotation of all the prin- 

 cipal plaiiets a length of day of fifty-seven hours and a half. (Report 

 of the British Assoc., 1850, p. xxxv.) 



t Beer and Madler, Beitrdge znr Phys. Kenntniss der Himl. Korper, 

 p. 104-106. Older and less certain observations by Hussey gave Jj. 



