The natural advantages which arise from the position of the earth which we inhabit with respect to the other planets, afford much employment to mathematical speculation; by which it has been discovered, that no other conformation of the system could have given such commodious distributions of light and heat, or imparted fertility and pleasure to so great a part of a revolving sphere.

It may be, perhaps, observed by the moralist, with equal reason, that our globe seems particularly fitted for the residence of a being, placed here only for a short time, whose task is to advance himself to a higher and happier state of existence, by unremitted vigilance of caution, and activity of virtue.

The duties required of man are such as human nature does not willingly perform, and such as those are inclined to delay who yet intend some time to fulfil them.  It was, therefore, necessary that this universal reluctance should be counteracted, and the drowsiness of hesitation wakened into resolve; that the danger of procrastination should he always in view, and the fallacies of security be hourly detected.

To this end all the appearances of nature uniformly conspire.  Whatever we see on every side reminds us of the lapse of time and the flux of life.  The day and night succeed each other, the rotation of seasons diversifies the year, the sun rises, attains the meridian, declines, and sets; and the moon every night changes its form.

The day has been considered as an image of the year, and the year as the representation of life.  The morning answers to the spring, and the spring to childhood and youth; the noon corresponds to the summer, and the summer to the strength of manhood.  The evening is an emblem of autumn, and autumn of declining life.  The night with its silence and darkness shows the winter, in which all the powers of vegetation are benumbed; and the winter points out the time when life shall cease, with its hopes and pleasures.

He that is carried forward, however swiftly, by a motion equable and easy, perceives not the change of place but by the variation of objects.  If the wheel of life, which rolls thus silently along, passed on through undistinguishable uniformity, we should never mark its approaches to the end of the course.  If one hour were like another; if the passage of the sun did not show that the day is wasting; if the change of seasons did not impress upon us the flight of the year; quantities of duration equal to days and years would glide unobserved.  If the parts of time were not variously coloured, we should never discern their departure or succession, but should live thoughtless of the past, and careless of the future, without will, and perhaps without power, to compute the periods of life, or to compare the time which is already lost with that which may probably remain.

But the course of time is so visibly marked, that it is observed even by the birds of passage, and by nations who have raised their minds very little above animal instinct:  there are human beings whose language does not supply them with words by which they can number five, but I have read of none, that have not names for day and night, for summer and winter.