1878.] 
Past Changes in the Universe. 
373 
the real dignity of Science, and theories, however elaborated, 
if vague, have no real dignity; and the aim ought surely to 
be to endeavour to think out the simplest method of arriving 
at a result, keeping in view the facft that simplicity is neces- 
sary to the orderly working of mechanical processes, and 
that the real point to admire is a simple method of attaining 
a mechanical result, because it is unique , not a complicated 
method (whishi may be conceived to be indefinitely varied). 
The beautiful kinetic theory of gases affords the simplest 
method to the solution of the problem of the constitution 
of the physical media in space, and in the case of the gra- 
vific medium it may be proved to be the only solution which 
can harmonise with observed fadls.* 
When we realise the practically unlimited intensity of the 
concealed energy that may thus exist in space (in the simple 
form of finely subdivided matter possessing a high velocity) 
one may cease to wonder at the sudden energy transferred 
to a mass of gunpowder (or a shell) in the adt of explosion, 
and realise how this otherwise incomprehensible and extra- 
ordinary effedt can take place. It would be illogical to 
consider a fadt less extraordinary, or that a rational expla- 
nation for it is less urgent, because it is commonplace, and 
precisely because there is this tendency it ought to be spe- 
cially guarded against. In the case of the explosion we 
have in principle simply the transference of motion from 
minute particles of matter (where the motion is therefore 
invisible) to grosser matter, in the form of clouds of vapour 
and palpable fragments of matter (when the motion is 
visible) ; and therefore to the superficial bodily eye there 
naturally appears to be an actual creation of motion. If the 
motion (before transference) were not invisible, it would not 
be mechanically efficient for the objedh to be attained ; for 
unless the moving particles of matter constituting the me- 
dium were small, it would be impossible to concentrate a 
considerable intensity of energy within a small volume of 
space. In the case of any powerful or intense motive 
source, velocity of the particles must evidently be relied on 
rather than mass (since mass occupies space, and prevents 
concentration of the energy. ' There could be no logical 
ground why problems of this nature should be regarded in 
* It may be observed that in the case of any medium constituted according 
to the kinetic theory, the velocity of the particles of the medium is equal to 
the velocity of propagation of a wave in the medium— 
X-4. 
V5 
See result appended by Prof, Maxwell to paper “ On the Mode of Propagation 
of Sound” (Philosophical Magazine, June, 1877). 
