*
[footnote] *Laplace, 'Expos. du Syst. du Monde', p. 270; 'M??canique
C??leste', t. ii., p. 169 and 171; Schubert, 'Astr.', bd. iii., ?ยค 206.
This limitation of the solar atmosphere in its present concentrated
condition is especially remarkable when we compare the central body of our
system with the nucleus of other nebulous stars. Herschel has discovered
several, in which the radius of the nebulous matter surrounding the star
appeared at an angle of 150". On the assumption that the parallax is not
fully equal to 1", we find that the outermost nebulous layer of such a star
must be 150 times further from the central body than our Earth is from the
Sun. If, therefore, the nebulous star were to occupy the place of our Sun,
its atmosphere would not only include the orbit of Uranus, but even extend
eight times beyond it.??
[footnote] *Arago, in the 'Annuaire', 1842, p. 408. Compare Sir John
Herschel's considerations on the volume and faintness of light of planetary
nebul??, in Mary Somerville's 'Connection of the Physical Sciences', 1835,
p. 108. The opinion that the Sun is a nebulous star, whose atmosphere
presents the phenomenon of zodiacal light, did not originate with Dominicus
Cassini, but was first promulgated by Mairan in 1730 ('Trait?? de l'Aurore
Bor.
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