to shape itself towards that remarkable
final stage which has points of resemblance to the initial stage. The
moon still continues to revolve in an orbit with a diameter steadily,
though very slowly, growing. The length of the month is accordingly
increasing, and the rotation of the earth being still constantly
retarded, the length of the day is also continually growing. But the
ratio of the length of the month to the length of the day now exhibits a
change. That ratio had gradually increased, from unity at the
commencement, up to the maximum value of somewhere about twenty-nine at
the epoch just referred to. The ratio now begins again to decline, until
we find the earth makes only twenty-eight rotations, instead of
twenty-nine, in one revolution of the moon. The decrease in the ratio
continues until the number twenty-seven expresses the days in the month.
Here, again, we have an epoch which it is impossible for us to pass
without special comment. In all that has hitherto been said we have been
dealing with events in the distant past; and we have at length arrived
at the present state of the earth-moon system. The days at this epoch
are our well-known days, the month is the well-known period of the
revolution of our moon. At the present time the month is about
twenty-seven of our days, and this relation has remained sensibly true
for thousands of years past. It will continue to remain sensibly true
for thousands of years to come, but it will not remain true
indefinitely. It is merely a stage in this grand transformation; it may
possess the attributes of permanence to our ephemeral view, just as the
wings of a gnat seem at rest when illuminated by the electric spark; but
when we contemplate the history with time conceptions sufficiently ample
for astronomy we realise how the present condition of the earth-moon
system can have no greater permanence than any other stage in the
history.

Our narrative must, however, now assume a different form. We have been
speaking of the past; we have been conducted to the present; can we say
anything of the future? Here, again, the tides come to our assistance.
If we have rightly comprehended the truth of dynamics (and who is there
now that can doubt them?), we shall be enabled to make a forecast of the
further changes of the earth-moon system. If there be no interruption
from any external source at present unknown to us, we can predict--in
outline, at all events--the subsequent career o