THE PLANET SATURN IN JULY 1869. 
257 
I SO wrote, that at the time of full moon the hemisphere we see 
(or a part of that hemisphere) is subjected to a heat exceeding 
that of boiling water. An enormous amount of heat poured in 
this way upon the surface of a planet would be rendered latent 
in transmitting but a small portion of the solidified gases into 
the aerial form, and produce no effects observable to us on 
earth ; just as the full heat of a tropical summer’s day poured 
for hours on the peaks of the Himalayas, produces no change 
which the inhabitant of the valleys can perceive, on the snowy 
masses lying there. If this view were just, we should learn to 
look upon all the satellites throughout the solar system as in a 
somewhat similar state to that of our own moon ; and at first 
sight the members of the Saturnian rings would appear, on 
account of their extreme minuteness, to be of all others those in 
which the cold would be most intense. But then a circumstance 
comes to be considered which would have an effect the other 
way. It is a part of the theory of the motions of satellite- 
rings, that there would be continual collisions among the mem- 
bers. I have shown in full, in chapter v. of my treatise on 
Saturn, how these collisions would arise and how they would 
operate upon the figure of the ring-system. There would be a 
gradual increase of width, chiefly through the approach of the 
inner edge of the rings towards the planet ; and there would 
also be a tendency to the formation of new rings within those 
already formed. But the true significance of these changes is 
this, that the whole system must be continually undergoing a 
loss of vis viva. Every collision involves such a loss, and the 
increase in the width of the system is in a sense a measure of 
the amount of loss. But this increase of width, though indicat- 
ing, does not compensate for, the loss of vis viva. There is 
only one way in which the loss can be compensated, and that 
way is indicated in a passing manner, in a note at p. 126 of my 
treatise on Saturn. There must be a continual generation of 
heat corresponding exactly to the loss of vis viva. Now this 
heat must tend to render the condition of all the satellites of 
the system very different from that of one of the ordinary at- 
tendants upon a planet. For all must partake in the distribu- 
tion of this heat ; because it is absolutely impossible that any 
single satellite can have an orbit which, even for a few hours, 
can keep it free from collision with one or more of its fellows. 
Thus every satellite is kept warm, so to speak, by a process of 
continual friction, and no such process of refrigeration as I 
conceive to have taken place upon the moon, can come into 
operation upon the satellites forming Saturn’s rings. Nay, it 
may well be that the heat of these bodies is very much greater 
than the mean heat of our earth’s surface. For processes of 
collision fully equal to the generation of sucli heat might be in 
