specific gravity, and
rapid rotation, obviously from the first threw the "superior" planets
into a class apart; and modern research has added qualities still more
significant of a dissimilar physical constitution. Jupiter, a huge globe
86,000 miles in diameter, stands pre-eminent among them. He is, however,
only _primus inter pares_; all the wider inferences regarding his
condition may be extended, with little risk of error, to his fellows;
and inferences in his case rest on surer grounds than in the case of the
others, from the advantages offered for telescopic scrutiny by his
comparative nearness.

Now the characteristic modern discovery concerning Jupiter is that he is
a body midway between the solar and terrestrial stages of cosmical
existence--a decaying sun or a developing earth, as we choose to put
it--whose vast unexpended stores of internal heat are mainly, if not
solely, efficient in producing the interior agitations betrayed by the
changing features of his visible disc. This view, impressed upon modern
readers by Mr. Proctor's popular works, was anticipated in the last
century. Buffon wrote in his _Epoques de la Nature_ (1778):[1039]--"La
surface de Jupiter est, comme l'on sait, sujette a des changemens
sensibles, qui semblent indiquer que cette grosse planete est encore
dans un etat d'inconstance et de bouillonnement."

Primitive incandescence, attendant, in his fantastic view, on planetary
origin by cometary impacts with the sun, combined, he concluded, with
vast bulk to bring about this result. Jupiter has not yet had time to
cool. Kant thought similarly in 1785;[1040] but the idea did not commend
itself to the astronomers of the time, and dropped out of sight until
Mr. Nasmyth arrived at it afresh in 1853.[1041] Even still, however,
terrestrial analogies held their ground. The dark belts running parallel
to the equator, first seen at Naples in 1630, continued to be
associated--as Herschel had associated them in 1781--with Jovian
trade-winds, in raising which the deficient power of the sun was
supposed to be compensated by added swiftness of rotation. But opinion
was not permitted to halt here.

In 1860 G. P. Bond of Cambridge (U.S.) derived some remarkable
indications from experiments on the light of Jupiter.[1042] They showed
that fourteen times more of the photographic rays striking it are
reflected by the planet than by our moon, and that, unlike the moon,
which sends its densest rays from the margi