30 
physical forces, followed by the discovery of the mechanical 
equivalent of heat by Dr. Joule, and by the molecular and 
atomic theories, has opened to Science even a wider field than 
was opened by Newton's use of the law of gravitation. In 
this new development of Science a principle is accepted which 
was recognised by Newton as an interpretation of his Third 
Law of Motion, but which it remained for modern Science to 
propound in the present form of conservation of energy ; viz., 
“ that in any system of bodies whatever to which no energy is 
communicated by external bodies, and which parts with no 
energy to external bodies, the sum of the various potential and 
kinetic energies remains for ever unaltered." This is really 
only another form of that principle of continuity which we 
found in the First Law of Motion, though in this modern 
form it is more than ever apparent that the continuity cannot 
be accepted as a self-evident axiom. Indeed, this law of 
the conservation of energy is as luminous an instance as could 
be found anywhere, of Science being compelled to assume a 
principle which it can never absolutely prove, but which it 
verifies as far as it can by observation of the results obtained 
on the assumption. It cannot be proved as a proposition 
in Euclid is proved.* The difficulty of proving it experi- 
mentally is even greater than that of proving the First Law of 
Motion by direct experiment. Strong indirect confirmation 
of its truth can be obtained, and whenever the law can be 
brought to the test of experiment it is found true. But what 
is it (we may ask) that in the absence of anything approaching 
complete proof satisfies the scientific mind as to the universal 
truth of the law ? Undoubtedly the conviction that permanence 
or continuity is a fundamental principle of the universe ; or, as 
Religion would express it, that the universe subsists in God. 
21. But this law of the conservation of energy, which is the 
result of further insight by science into the consecutive order 
of the universe, is followed by another law which, to the un- 
scientific mind, appears like a contradiction of the former, 
viz., the dissipation of available energy. While the conserva- 
tion of energy points to permanence, this indicates a process 
of dissolution ; that is, unless it should be checked (as Clerk 
Maxwell has shown to be possible) by the interposition of 
intelligence. I notice this because, though not directly 
bearing on my present argument, it both strengthens it and 
nearly affects the general question of the relation between 
Science and Religion. Were it not for this, second law, which 
indicates that the present visible universe has had a beginning 
* See Conservation of Energy , by Balfour Stewart. 
