to the Presence of a Medium pervading all Space.. 509 
Besides the valid objections which Professor Maxwell urges 
against the common idea which regards the rings as two flat 
solids, others of a somewhat different character have been 
suggested by Mr. Bond, who has embraced the opinion that the 
ring is fluid. But whatever be its composition, or whatever 
proportions of fluid and solid matter it may consist of, all its 
parts must have independent movements around Saturn, and 
velocities depending on their distance from his centre. The 
attraction of the planet will be an insurmountable obstacle to 
their conversion into satellites, and will even prevent them from 
concentrating in excessive numbers in any locality; but their 
incessant action must be attended with a constant development 
of heat and a gradual destruction of motion. In consequence 
of the necessary alteration in the orbit of its parts from this 
cause, the dimensions of the ring cannot always remain the 
same ; and though it is not likely that the nearest edge is ap- 
proaching the planet so rapidly as the researches of Struve 
and Hansen would indicate, yet, as some change of this nature 
is unavoidable, we cannot resist the conclusion that the rings 
have been introduced into the zone which they now occupy, 
from one in which their matter could only exist im the form of 
two satellites. Accordingly there appears to be no ground 
for any other inference than that I have adopted, in regard 
to the imperceptible diminution of the orbits of secondary 
planets by the action of a resisting medium. 
In tracing the ultimate effects of a similar impediment to 
motion in the dark systems of remote space, we deduce so satis- 
factory an explanation of the temporary stars, that we may regard 
these celestial apparitions as indicating the existence of the 
same ethereal fluid, and manifesting the great revolutions to 
which it leads in the condition of the heavenly bodies. In my 
last article, I have shown that the instantaneous manner in 
which a secondary or a primary planet must undergo a total 
dismemberment on coming into fatal proximity with the central 
sphere harmonizes in a very decided manner with the astonish- 
ing rapidity with which temporary stars attain their greatest 
brillancy. This peculiarity, taken in connexion with the com- 
paratively slow and gradual decline, is sufficient to set aside the 
theory which ascribes such ephemeral exhibitions of light to the 
rotation of great orbs, self-luminous on one side and dark on 
the other. But this theory, though adopted by Arago and 
other eminent astronomers, is liable to a more fatal objection. 
This will be apparent when we investigate the circumstances 
necessary to make a partially luminous sphere or spheroid display 
its brilliancy to the inhabitants of the earth for only seven- 
teen months, while its period of rotation has been estimated ‘at 
