~ On the Presence of a Medium pervading all Space. 507 
magnetic force. In the same light I regard the experiments of 
Professor Wiedemann, mentioned in vol. xi. No. 42 of the ‘ Pro- 
ceedings of the Royal Society,’ the results of which point to the 
same conclusion. 
Cambridge Observatory, 
May 22, 186]. 
ney 
LXXIV. On Phenomena which may be traced to the Presence of 
a Medium pervading all Space. By Daniex VauGHAN. 
i the permanent change which seems to have been detected 
in the revolution of Encke’s comet be not sufficient to 
establish the doctrine of a space-pervading ether, it may afford 
reasonable motives for examining other indications of the im- 
pediments of such a fluid to celestial motion. The direct in- 
formation which can be obtained on this subject is at present very 
limited and uncertain. The approximate investigations hitherto 
given by mathematicians of the cause of the perturbation of the 
planets, necessarily overlook many slight effects of their mutual 
attraction ; and we are thus prevented from discovering the un- 
periodical changes which a small resistance to their movements 
might occasion. In addition to this, we are ncommoded by the 
want of observations made during very long periods of time; for 
these are as necessary in tracing the course of remote physical 
events, as an extensive base-line is in determining the distances 
of the fixed stars. But by investigating the necessary conse- 
quence of a resisting medium, and testing the result by a com- 
parison with observed facts, we may be enabled to base our con- 
clusions respecting this important question on evidence no less 
satisfactory than that which has already served to establish many 
of the received doctrines of physical science. 
As there has prevailed among some astronomers an impression, 
not unwholly unfounded, in regard to a modification which the 
sun’s attractive power 1s supposed to experience from the emis- 
sion of his light, it seems advisable to give special attention to 
cases in which the central body is not luminous; and certain 
phenomena, observed in the secondary systems and in the dark 
systems of space, afford evidence not vitiated by any effects which » 
light might be expected to produce. In my communication in 
the Philosophical Magazine for last April, 1 showed that a 
satellite impeded by the resistance of a medium would, by an im- 
perceptibly slow diminution of its orbit, be finally introduced 
into the region of instability, where its dismemberment must be 
inevitable, and where it must be transformed into a ring, similar 
* Communicated by the Author. 
