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matical investigations,, by wbicb from Newtoffis time the results 
of the law of gravitation have been determined, are founded 
on three Laws of Motion, as they are called. What are these ? 
Are they self-evident axioms which reason cannot question 
without self-contradiction ? or are they assumptions necessary 
to Science, which it verifies, so far as it is able, within the 
limited range of our experience, from the agreement with 
observation of the conclusions made on that assumption ? The 
fact that the truth of these laws was so long questioned and 
so slowly apprehended by the human mind, sufficiently indi- 
cates that they are not self-evident identities. Let us take 
the first and simplest of these laws. A body at rest will con- 
tinue at rest, and a body in motion will continue to move with 
the same velocity in the same direction, unless acted on by 
some extraneous force or cause of motion. In other words, it 
continues in the same state as regards motion, unless there is 
some cause of change of state. Now the principle of con- 
tinuity, which is assumed here, to those of us who are familiar 
with it in the dynamical problems of the universe, and with 
the necessity of it to all scientific investigation, may appear 
almost self-evident. But if we should be asked on what grounds 
we have this conviction, independent of the very incomplete evi- 
dence that Nature supplies, we certainly could not answer, as we 
must with regard to a mathematical axiom, that it expresses an 
identity. The existence of a state and its continuance are two 
totally different ideas. We must look further for the reason 
why we assume continuity. Religion points us to a sufficient 
and rational basis, viz., that Nature subsists in One Who is 
eternal and unchangeable, and both its continuity and its 
changes have their adequate cause in Him. Is there any other? 
18. This principle, in fact, involves a second, viz., that in 
Nature there is no self-causation. The second law of motion, 
which has sometimes been called “ the law of independence,” 
affirming that the effects of forces, or causes of motion, are 
under all circumstances equivalent to those causes, enlarges 
this view. The result of the various causes acting together 
can be neither more nor less than if they acted separately. 
Whether the particle on which they act is at rest or in motion 
does not affect this. Neither the state of the body, nor the 
combination of the causes, alter the law of causation. In other 
words, matter is merely inert or passive. There is no power 
in it either to generate motion or to change motion. We are 
driven, therefore, to look for an original cause of motion out of 
the material universe. And if of motion, how much more of 
life, sensation, consciousness, intelligence ? For it is absurd to 
suppose that matter cannot generate motion in itself, and yet 
