- 
162 Screntifie Intelligence. 
Now a large planet has both more energy of rotation and mo 
angular momentum; hence it is to be expected that large shail 
should proceed in their changes more slowly than small ones. 
ars is the smallest of the planets, which are attended by sat- 
ellites, and it is here alone that we find a satellite revolving faster 
than the planet rotates. This will also be the ultimate fate of our 
moon, because after the joint lunar and solar tidal friction has 
reduced the earth’s rotation to an identity with the moon’s orbital 
motion, the solar tidal friction will continue to reduce it still fur- 
ther, so that the earth will rotate faster than the moon revolves. 
Befo ore, however, this can take place with us, the moon must 
recede to an en ormo ous distance from the earth, and the earth 
must rotate in forty or fifty days instead of in twenty-four hours. 
But the satellites of Mars are so small, that they would only 
recede a very short way from the planet, before the solar tidal 
friction reduced the planet’s rotation below the satellite’s revolu- 
tion. The rapid revolution of the inner satellite of Mars may 
then, in a sense, be considered as a memorial of the primitive 
rotation of the planet round its axis. 
The planets Jupiter and Saturn are very much larger than the 
earth, and here we find the planets rotating with thee speed, and 
the satellites revolving with short periodic tim The inclina- 
tions of the orbits of Jupiter’s satellites to their ey proper planes 
are very interesting from the point of view of the present theory. 
The Saturnian system is much more complex than that of 
upiter, and it seems partially in an early stage of development 
an partially far advanced. 
he details of the motions of the satellites are scarcely well 
enough hitiwn to afford strong arguments either for or against 
the theory. 
I have not as yet investigated the case of a planet or star 
attended by several satellites, but perhaps future investigations 
may throw further light both on the case of Saturn, and on the 
whole solar system itse 
The celebrated nebular hypothesis of ae and Kant 
oses that a revolving nebula detached a ring, which ultiasnieely 
fedanie consolidated into a planet or satellite, and that the centr “ 
portion of the nebula continued to ¢ ontract, 
nucleus of the sun or planet. The theory now proposed is a con- 
ro modification of this view, for it supposes that the rup- 
re of the central body did not take place until it was partially 
eomeatidated: and had attained nearly its present dime ensions. 
2. 7 Jan and the Planets.—Mr. J. Delauney has pre 
sented to the Paris Academy of Sciences some new re esults 
