10 The Saturnian System. [January ; 
Jovian satellite systems lie far within the limits of the 
spheres ruled over with superior sway by these planets 
respectively. For it will be remembered that Saturn’s 
sphere of sway has a diameter of about 29,500,000 miles, 
while Jupiter’s (see note at p. 7) is about 200,000 miles 
wider. The effect of this is seen in the motions of the 
Jovian and Saturnian satellite systems. For whereas the 
orbit of our moon around the sun is everywhere concave 
towards the sun, notwithstanding the motion of the moon 
round the earth, the paths even of the outermost of the 
Jovian and Saturnian satellites are markedly convex towards 
the sun when these bodies are in inferior conjunction. The 
inner satellites, in fact, not only move at those times on 
courses convex towards the sun, but have an excess of 
motion in their orbit round their primary over the onward 
motion which they share with him around the sun, and 
consequently travel backwards in this part of their motion. 
It follows that in successive lunations the inner satellites 
trace out looped paths. This happens with the four 
satellites Mimas, Euceladus, Tethys, and Dione. ‘The 
fifth, Rhea, shows the singular peculiarity of coming almost 
exactly to rest when in inferior conjun¢tion—that is, to rest 
relatively to the solar system. The path of this satellite 
with reference to the solar system is nearly an epicycloid, 
any portion of which, from cusp to cusp, is appreciably a 
cycloid. ‘The satellites Titan, Hyperion, and Japetus follow 
waved courses convex to the sun through a considerable 
portion of each lunation. It will be seen that Saturn 
has his system in complete control.* Even the outermost 
is very much less perturbed by the sun (relatively as well as 
absolutely) than our moon. 
The second satellite inwards has an orbit diameter of 
rather more than two millions of miles. It is a somewhat 
remarkable circumstance that this satellite, lying between 
Titan and Japetus, the two largest satellites, should be the 
smallest or at least the faintest of all Saturn’s satellite 
* The distinction between our moon and the satellites of the major planets is 
a marked one, and significant. Our moon is, in point of fact, much more to be 
regarded as a fifth planet of the inner family of terrestrial planets than as an 
orb dependent on ourearth. If she could be watched from a distant standpoint, 
her motions would scarcely indicate the fact that she circles around the earth; 
for, in fact, the result of this so-called circling motion corresponds simply to large 
perturbational effects. _Onthe contray, the motions of the satellites of Jupiter, 
Saturn, Uranus, and Neptune, are chiefly influenced by their respective 
primaries, and this could not but be recognised if the motions of these moons 
were watched from a distant point. Even if their primaries were concealed 
during the observation, the motions of the satellites would reveal the fact that 
these bodies are ruled by a central orb. 
