plished a single revolution. It is, however, only necessary for
us to note those stages of the mighty progress which correspond to
special events. The first of such stages was attained when the month
assumed its maximum ratio to the day. At this time, the month was
about twenty-nine days, and the epoch appears to have occurred at a
comparatively recent date if we use such standards of time as tidal
evolution requires; though measured by historical standards, the epoch
is of incalculable antiquity. I cannot impress upon you too often the
enormous magnitude of the period of time which these phenomena have
required for their evolution. Professor Darwin's theory affords but
little information on this point, and the utmost we can do is to
assign a minor limit to the period through which tidal evolution has
been in progress. It is certain that the birth of the moon must have
occurred at least fifty million years ago, but probably the true
period is enormously greater than this. If indeed we choose to add a
cipher or two to the figure just printed, I do not think there is
anything which could tell us that we have over-estimated the mark.
Therefore, when I speak of the epoch in which the month possessed the
greatest number of days as a recent one, it must be understood that I
am merely speaking of events in relation to the order of tidal
evolution. Viewed from this standpoint, we can show that the epoch is
a recent one in the following manner. At present the month consists of
a little more than twenty-seven days, but at this maximum period to
which I have referred the month was about twenty-nine days; from that
it began to decline, and the decline cannot have proceeded very far,
for even still there are only two days less in the month than at the
time when the month had the greatest number of days. It thus follows
that the present epoch--the human epoch, as we may call it--in the
history of the earth has fallen at a time when the progress of tidal
evolution is about half-way between the initial and the final stage. I
do not mean half-way in the sense of actual measurement of years;
indeed, from this point it would seem that we cannot yet be nearly
half-way, for, vast as are the periods of time that have elapsed since
the moon first took its departure from the earth, they fall far short
of that awful period of time which will intervene between the present
moment and the hour when the next critical state of earth-moon
history shal