Many reasons, on the contrary, might be invoked which tend to compel us to see in nature phenomena which cannot be reduced to movement.
Mechanics as ordinarily understood is the study of reversible phenomena.

If there be given to the parameter which represents time,[1] and which has assumed increasing values during the duration of the phenomena, decreasing values which make it go the opposite way, the whole system will again pass through exactly the same stages as before, and all the phenomena will unfold themselves in reversed order.

In physics, the contrary rule appears very general, and reversibility generally does not exist.

It is an ideal and limited case, which may be sometimes approached, but can never, strictly speaking, be met with in its entirety.

No physical phenomenon ever recommences in an identical manner if its direction be altered.