Nebular Theory. — Mistocklcs. 369 
moons is the combined attraction of himself and his inner 
moons. This latter factor is of considerable importance, since 
one of the moons, Titan, is of about the same size as the 
planet Mars. This is true of all large planets with many 
moons and of Ihe Sun as well as the planets. The velocity of 
Uranus, for instance, which is 258 miles a minute, would be 
about 300 miles less a day. if it were not for Jupiter. 
As answer to the question, how near a small planet must 
come to Jupiter in order to be attracted by him we need 
only call attention to the fact that Jupiter is two-fifths 
stronger than Saturn, and that the power of the Sun's attrac- 
tion is about two-eighths stronger in his orbit than in Sat- 
urn's. l""rom this we find, that Saturn, if placed in Jupiter's 
orbit, would have lost about two-eighths or 7 million miles 
of the radius within which he can now attract smaller 
planets, and that Jupiter himself exercises this influence at 
a distance of about 35 million miles in all directions from 
his center. 
If we next direct our attention to the most distant planets 
and notice that Neptune exerts a disturbing influence on the 
large planet Uranus, which is 1,000 million miles nearer 
the Sun, we find this natural order no less self-demonstrating. 
Since we know that Neptune disturbs Uranus, it is easy to 
see what the result would be, if a small body, say about the 
size of oui Moon, being -/jooo oi Uranus, came within a 
few million- miles of Neptune. Its capture as a moon would 
be absolutely certain. 
§16. The number of moons of the distant planets must, 
as a rule, stand in relation to the size of those planets and 
their distance from the Sun, no matter whether the moons 
have been discovered or not. The reason for this is a com- 
bination of several causes. As one of these causes we notice 
the increasing sphere of a planet's attractive power as its 
distance from the Sun increases. A second cause is the in- 
crease in the orbital excentricity of all the planets in pro- 
portion to their size and their distance from the Sun. A third 
factor is found in the circumstance, that the orbits of the 
minor planets are more analogous to the orbits of the larger 
ones the greater the distance from the Sun : this, again, be- 
ing caused by the diminution of the power of the light-stuff, 
