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ther renewal of our annual labours, to present a fuller developement of this interesting topic. The nature of this perpetual current, however, that is of time itself, we shall leave to those who are more deeply skilled in the abstruse subtilties of metaphysical investigations, and confine ourselves chiefly to illustrations of its varied relations to the inquiries of man, and its applications to the practical purposes of human life.

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There is, perhaps, no idea with which the mind is more familiar than that of time, and scarcely any thing which it is more difficult to define. Its intimate connection, however, with our very existence has always rendered a right understanding of this subject of great importance; and hence the interest it has so constantly excited among philosophers of all ages. The following selection will show with what success their attempts at a scientific definition have been attended. On this subject, St. Augustine said, that if not asked what time was, he knew; but if requested to define it, he did not know. Mr. Leibnitz defined time to be an order of successions, as space is an order of coexistences.' Hooke, as we have already stated, denominates time 'the flux of that instant in which the heavenly bodies began their motions.' Some modern speculators in metaphysical subtilties deny its existence altogether, and affirm that time is only a particular modification of eternity; which has no distinct or conceivable existence independent of the subject of which it is an attribute or property. So that, in order to gain a clear conception of the quality, we must first comprehend the subject to which it belongs; or, in plain terms, the finite must comprehend the infinite.

Dr. Young, in his Night Thoughts, has some curious poetical ideas on this subject. He calls time heaven's stranger, and represents its birth as G

coincident with the creation of the world. Thus, in one place, he says,

That memorable hour of wondrous birth,
When the dread Sire, on emanation bent,
And big with nature, rising in his might,

Called forth creation, (for then time was born)
By godhead streaming through a thousand worlds,

In another place, the same author mysteriously says,

From old eternity's mysterious orb

Was time cut off, and cast beneath the skies;
The skies, which watch him in his new abode,
Measuring his motions by revolving spheres ;
That horologe machinery divine.

Hours, days, and months, and years, his children, play
Like numerous wings around him, as he flies;

Or rather, as unequal plumes, they shape
His ample pinions, swift as darted flame,
To gain his goal, to reach his ancient rest,
And join anew eternity his sire.

These things have not been stated for the sake of the information they afford relative to the nature of time, abstractedly considered; but merely as specimens of the insuperable difficulties which obstruct the progress of the human mind when it attempts to pass the bounds which Infinite Wisdom appears to have set to its powers, and to consider what things are in themselves, instead of being satisfied with contemplating them in the relation they bear to one another, and to the other phenomena of nature. Maclaurin, whose mind was at once refined, penetrating, and comprehensive, when treating on this subject, does not attempt to define time as it is in itself, but only to illustrate our conceptions of it. From the succession of our own ideas (he observes), and from the successive variations of external objects in the course of nature, we easily acquire the ideas of duration and time, and of their measures. We conceive true or absolute time to

flow uniformly in an unchangeable course, which alone serves to measure with accuracy the change of all other things. For, unless we correct the vulgar measures of time, which are gross and inaccurate, by proper equations, the conclusions are always found to be incorrect and erroneous. Time may be conceived to be divided into successive parts, that may be less and less without end, though, with respect to any one particular being, there may be a least sensible time, as well as a minimum sensibile in other magnitudes. But however various the flux of time may appear to different intellectual beings, it cannot be thought to depend upon the idea of any created being whatever.'

Our ideas relative to the measure of time, therefore, include those of motion; and when a body describes equal spaces with a uniform velocity, we readily conceive that the times of their description are equal to each other, or that an equal interval of duration elapses between the commencement and termination of each motion. This may be familiarly illustrated by conceiving the minute hand of a watch to pass with a uniform motion over the whole circumference of the dial plate; then, all the divisions on that plate being supposed to be equal to each other, the time employed by the hand in passing over each of them must be the same, and each complete revolution of the hand will also be performed in the same time. Now, as the stars are fixed bodies at an immense distance from the Earth, and the diurnal rotation of the Earth is a uniform motion, this illustration may be readily transferred from the watch to the heavens; for, if we suppose an imaginary line to extend from any point on the Earth's surface to a star situated in the vertical plane passing through that point and the pole of the world, the termination of this line

would describe a circle in the heavens, with a uniform motion occasioned by the diurnal revolution of the Earth; and consequently not only every equal part of this circle would be described in an equal time, but each consecutive revolution would also be completed in precisely the same period of duration. This uniform revolution of the Earth on its axis, which causes any star always to return to the plane of the same meridian, after equal and successive intervals, therefore, becomes a proper measure of time, and one which the laws of nature appear to have rendered immutable. Each of these revolutions is denominated a sidereal day; and the measure of duration as referred to this standard is called sidereal time.

The Sun, however, is the most conspicuous object in the heavens, and therefore the best adapted for the division of time into periods for the common and practical purposes of life; and hence his successive returns to the same meridian, though after unequal intervals of duration, have generally been adopted. Duration, as thus measured by the apparent motion of the Sun, is denominated apparent or solar time, and each interval between two consecutive returns of the Sun to the same meridian constitutes a solar day, which is divided into 24 hours.

But as the Earth has an annual motion in its orbit as well as a diurnal rotation about its axis, it advances through a certain part of its orbit during each of its diurnal rotations; it must therefore have actually performed more than one complete revolution on its axis, before the Sun appears again on the same meridian; for the diurnal revolution of the Earth is evidently completed, when the plane of the terrestrial meridian becomes again parallel to its former position. If the Earth had not any motion in its orbit, the

time that elapsed between the Sun leaving any meridian, and arriving at that meridian again, would always be equal to the time in which it performed one complete revolution on its axis. But as the Earth moves nearly a degree in its orbit while it performs one diurnal revolution, the length of one of these revolutions must always be less than 24 hours, or the time which elapses between the arrival of the Sun at the meridian in two successive days. Instead of the Earth's motion in its orbit, if the Sun be supposed to move in an opposite direction, the effect will be the same. For when the Sun is in the meridian of any place on one day, and that place is carried round to the same position the next day, the Sun will have moved from his former situation; so that the place on the Earth must move through an additional arc before the Sun will again be in the meridian, and consequently it will have performed more than a complete revolution. The time which is occupied in describing this additional are will evidently be the same part of 24 hours, as the arc is of a whole revolution of the Sun round the Earth, or of 360°. Now the Sun in one day moves through an arc equal to 59' 8" 3; therefore we have 360°:59'8" 3 ::24h. 3m. 56s 6. Hence 24 h.-3 m. 56s G

23 h. 56 m. 3s4, the real time in which the Earth performs a revolution about its axis. As the stars do not change their places like the Sun, they appear to describe circles in the heavens, or to revolve about the Earth in 23 h. 56 m. 3s4; so that this is the length of the sidereal day, and 24 h. that of the solar day. Consequently, in 365 days, the Earth will perform just 366 complete revolutions about its axis.

[To be continued.]

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