n of their recurrence at
regular intervals. He concluded that the development of the deeper
tinges of colour, and of the equatorial "port-hole" markings girdling
the globe in regular alternations of bright and dusky, agreed, so far as
could be ascertained, with epochs of sun-spot maximum. The further
inquiries of Dr. Lohse at Bothkamp in 1873[1092] went to strengthen the
coincidence, which had been anticipated _a priori_ by Zoellner in
1871.[1093] Moreover, separate and distinct evidence was alleged by Mr.
Denning in 1899 of decennial outbreaks of disturbance in north temperate
regions.[1094] It may, indeed, be taken for granted that what Hahn terms
the universal pulse of the solar system[1095] affects the vicissitudes
of Jupiter; but the law of those vicissitudes is far from being so
obviously subordinate to the rhythmical flow of central disturbance as
are certain terrestrial phenomena. The great planet, being in fact
himself a "semi-sun," may be regarded as an originator, no less than a
recipient, of agitating influences, the combined effects of which may
well appear insubordinate to any obvious law.

It is likely that Saturn is in a still earlier stage of planetary
development than Jupiter. He is the lightest for his size of all the
planets. In fact, he would float in water. And since his density is
shown, by the amount of his equatorial bulging, to increase
centrally,[1096] it follows that his superficial materials must be of a
specific gravity so low as to be inconsistent, on any probable
supposition, with the solid or liquid states. Moreover, the chief
arguments in favour of the high temperature of Jupiter, apply, with
increased force, to Saturn; so that it may be concluded, without much
risk of error, that a large proportion of his bulky globe, 73,000 miles
in diameter, is composed of heated vapours, kept in active and agitated
circulation by the process of cooling.

His unique set of appendages has, since the middle of the last century,
formed the subject of searching and fruitful inquiries, both theoretical
and telescopic. The mechanical problem of the stability of Saturn's
rings was left by Laplace in a very unsatisfactory condition.
Considering them as rotating solid bodies, he pointed out that they
could not maintain their position unless their weight were in some way
unsymmetrically distributed; but made no attempt to determine the kind
or amount of irregularity needed to secure this end. Some observation