18. A good measure of time must divide its whole duration into equal periods.
In the measuring of extension,
there is nothing more required but the application of the standard or measure we make use of to the thing of
whose extension we would be informed. But in the measuring of duration this cannot be done, because no two
different parts of succession can be put together to measure one another. And nothing being a measure of duration
but duration, as nothing is of extension but extension, we cannot keep by us any standing, unvarying measure of
duration, which consists in a constant fleeting succession, as we can of certain lengths of extension, as inches,
feet, yards, etc., marked out in permanent parcels of matter. Nothing then could serve well for a convenient
measure of time, but what has divided the whole length of its duration into apparently equal portions, by
constantly repeated periods. What portions of duration are not distinguished, or considered as distinguished and
measured, by such periods, come not so properly under the notion of time; as appears by such phrases as these,
viz., "Before all time," and "When time shall be no more."
