is a vital condition of the existence of such a creature as man. The
revolution of the year, with its various incidents of summer and winter,
and seed-time and harvest, is not less involved in our social, material,
and moral progress. It is true that at the poles, and on the equator,
the effects of these revolutions are variously modified or wholly
disappear; but as the necessary consequence, human life is extinguished
at the poles, and on the equator attains only a languid or feverish
development. Those latitudes only in which the great motions and
cardinal positions of the earth exert a mean influence, exhibit man in
the harmonious expansion of his powers. The lunar period, which lies
at the foundation of the _month_, is less vitally connected with human
existence and development; but is proved by the experience of every age
and race to be eminently conducive to the progress of civilization and
culture.

But indispensable as are these heavenly measures of time to our life and
progress, and obvious as are the phenomena on which they rest, yet owing
to the circumstance that, in the economy of nature, the day, the month,
and the year are not exactly commensurable, some of the most difficult
questions in practical astronomy are those by which an accurate division
of time, applicable to the various uses of life, is derived from the
observation of the heavenly bodies. I have no doubt that, to the Supreme
Intelligence which created and rules the universe, there is a harmony
hidden to us in the numerical relation to each other of days, months,
and years; but in our ignorance of that harmony, their practical
adjustment to each other is a work of difficulty. The great
embarrassment which attended the reformation of the calendar, after the
error of the Julian period had, in the lapse of centuries, reached ten
(or rather twelve) days, sufficiently illustrates this remark. It is
most true that scientific difficulties did not form the chief obstacle.