8 OF THE USE AND ADVANTAGE

the several seasons of the Greeks ; and the risingof Sirius with the fun, announced to theEgyptians the overflowing of the Nile, and thecustomary time of sowing their grain, whichwas immediately after its retreat. Many of theancient Poets and Historians furnish us likewisewith instances of a similar kind, from which itappears, that some of the most powerful andpolished nations had, for a long time, no othercalendar than that which consisted of a fewsimple observations on the rising and setting ofcertain stars.

In most of the common affairs of life, nothingis more necessary than an exact measure of time.But how is this to be obtained ? W e have theidea of succession only from motion; and in or-der that the division of it into parts may be ac-curate, it is requisite that the motion should beconstant and uniform : but such a perfect andimmutable test is not to be found upon the earth.Man has in himself the principles of motion ;his sensations and ideas succeed one another ina certain order; but their durations and re-turns are so irregular, that he can by no. meansemploy them as a proper measure of time. Themind that suffers, and the mind that rejoices;the lover, courting his mistress, and the crimi-nal upon the rack, compute by very differentreckonings.

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