fe e5t 4 
XLV. 
OF THE KINETIC THEORY OF GAS, REGARDED AS 
ILLUSTRATING NATURE. By GEORGE JOHNSTONE 
STONEY, M.A., D.Sc., F.R.S., Vice-President, Royal Dublin 
Society. 
[Read June 26; Received for publication Junz 28; Published August 17, 1895.] 
ScrencE may be defined as the investigation of how nature works, 
of how and why events in nature occur. 
This investigation is best carried on by employing the Physical 
Hypothesis, viz. that the objects of nature act on one another, 
either directly (action at a distance), or through intervening media 
(which by many is supposed to be an essentially different kind of 
action). Now, the objects of nature, in the more strict sense of 
that phrase, are syntheta of human perceptions and ultra-percep- 
tions ; and syntheta of perceptions cannot be what really act. 
Nevertheless, it is eminently useful to carry on our investigation 
under the physical hypothesis that it is they which act, and to 
confine our efforts to tracing out what effects this action must be 
supposed capable of producing, and under what laws it must 
_ operate, in order that it may account for what occurs in nature. 
This, however, is felt by many persons to be too abstract an 
attitude of mind; and to satisfy them, and create the plausibility 
which they demand, by relieving the fundamental conceptions of 
what is oppressively felt as the absurdity of supposing that syn- 
theta of perceptions act, it is usual to supplement these syntheta 
by piling an aérial Pelion upon this solid Ossa, and by supposing 
that in addition to the sensible object which occupies any portion 
of space there is what is called its material substance occupying 
the same position, which, partly directly and partly by its motions, 
acts on other material substances [the ether being one of these 
material substances]. According to this, which is the prevalent 
hypothesis among both scientific and non-scientific men, it is these 
substances which travel about through space; and the sensible 
