Their confidence in the value of the processes they had seen employed was exaggerated, and their mistrust of the future unjustified.

This example shows how imprudent it is to endeavour to fix limits to progress.

It is an error to think the march of science can be stayed; and in reality it is now known that the ten-millionth part of the quarter of the terrestrial meridian is longer than the metre by 0.187 millimetres.

But contemporary physicists do not fall into the same error as their forerunners, and they regard the present result as merely provisional.

They guess, in fact, that new improvements will be effected in the art of measurement; they know that geodesical processes, though much improved in our days, have still much to do to attain the precision displayed in the construction and determination of standards of the first order; and consequently they do not propose to keep the ancient definition, which would lead to having for unit a magnitude possessing the grave defect from a practical point of view of being constantly variable.
We may even consider that, looked at theoretically, its permanence would not be assured.