6 THOUGHTS ON NATURAL PHILOSOPHY. 
the logicians come in, and it is their high duty to test the 
reasoning of the philosophers. If that reasoning cannot 
stand the necessary tests, the philosophy must be cast aside, 
no matter who may be its author. The work of the logician 
is necessary, because some of the suggestions of learned men 
are fit only for Alice in Wonderland, where a thing can be a 
pussy-cat and not a pussy-cat at the same time. 
Sir Isaac Newton himself appears to have had his doubts. 
He at one time thought of endeavouring to account for 
orbital phenomena by differences of pressure in the ether, 
but did not publish a theory on the subject. 
In Newton’s Principia the first law is that “ Every body 
continues in its state of rest or of uniform motion in a 
straight line, except in so far as it may be compelled by 
impressed forces to change that state.”’ 
Let us transpose the wording as follows:—Every body 
continues in its state of uniform motion in a straight line, 
or in its state of rest, except in so far as it may be compelled 
by impressed forces to change that state. 
The reason that the law as transposed is more correctly 
stated is as follows: It is acknowledged by scientific inquirers 
that in scientific matters we must reason from the known 
to the unknown. The only state of rest known to us is a 
relative and occasional state. Take a book between the 
two hands, apply an upward and a downward pressure; 
when the pressure is equal in opposite directions a state of 
equilibrium will result, and the book will be at rest. The 
force that causes this state of rest is energy exercised in 
opposite directions. What is true of the book is true of 
other matter. Energy (or material motion) causes the state 
of rest, therefore energy (or material motion) must be the 
original thing, and rest a secondary matter or effect. To 
take the effect as the basis of an argument or system of 
6 
* 
