TIME

, a succession of phenomena in the universe; or a mode of duration, marked by certain periods and measures; chiefly indeed by the motion | and revolution of the luminaries, and particularly of the sun.

The idea of Time in general, Locke observes, we acquire by considering any part of infinite duration, as set out by periodical measures: the idea of any particular Time, or length of duration, as a day, an hour, &c, we acquire first by observing certain appearances at regular and seemingly equidistant periods. Now, by being able to repeat these lengths or measures of Time as often as we will, we can imagine duration, where nothing really endures or exists; and thus we imagine tomorrow, or next year, &c.

Some of the later school-philosophers define Time to be the duration of a thing whose existence is neither without beginning nor end: by this, Time is distinguished from eternity.

Aristotle and the Peripatetics define it, numerus motus secundum prius & posterius, or a multitude of transient parts of motion, succeeding each other, in a continual flux, in the relation of priority and posteriority. Hence it should follow that Time is motion itself, or at least the duration of motion, considered as having several parts, some of which are continually succeeding to others. But on this principle, Time or temporal duration would not agree to bodies at rest, which yet nobody will deny to exist in Time, or to endure for a Time.

To avoid this inconvenience, the Epicureans and Corpuscularians made Time to be a sort of flux different from motion, consisting of infinite parts, continually and immediately succeeding each other, and this from eternity to eternity. But others directly explode this notion, as establishing an eternal being, independent of God. For how should there be a flux before any thing existed to flow? and what should that flux be, a substance, or an accident? According to the philosophic poet, “Time of itself is nothing, but from thought Receives its rise; by labouring fancy wrought From things consider'd, whilst we think on some As present, some as past, or yet to come. No thought can think on Time, that's still confest, But thinks on things in motion or at rest.” And so on. Vide Lucretius, book i.

Time may be distinguished, like place, into absolute and relative.

Absolute Time, is Time considered in itself, and without any relation to bodies, or their motions.

Relative or Apparent Time, is the sensible measure of any duration by means of motion.

Some authors distinguish Time into astronomical and civil.

Astronomical Time, is that which is taken purely from the motion of the heavenly bodies, without any other regard.

Civil Time, is the former Time accommodated to civil uses, and formed or distinguished into years, months, days, &c.

Time makes the subject of chronology.

Time

, in music, is an affection of sound, by which it is said to be long or short, with regard to its continuance in the same tone or degree of tune.

Musical Time is distinguished into common or duple Time, and triple Time.

Double, duple, or common Time, is when the notes are in a duple duration of each other, viz, a semibreve equal to 2 minims, a minim to 2 crotchets, a crotchet to 2 quavers, &c.

Common or double Time is of two kinds. The first when every bar or measure is equal to a semibreve, or its value in any combination of notes of a less quantity. The second is where every bar is equal to a minim, or its value in less notes. The movements of this kind of measure are various, but there are three common distinctions; the first slow, denoted at the beginning of the line by the mark C; the 2d brisk, marked thus ; and the 3d very brisk, thus marked .

Triple Time is when the durations of the notes are triple of each other, that is, when the semibreve is equal to 3 minims, the minim to 3 crotchets, &c. and it is marked T.

Time-keepers, in a general sense, denote instruments adapted for measuring time. See Chronometer.

In a more peculiar and definite sense, Time-keeper is a term first applied by Mr. John Harrison to his watches, constructed and used for determining the longitude at sea, and for which he received, at different times, the parliamentary reward of 20 thousand pounds. And several other artists have since received also considerable sums for their improvements of Time-keepers; as Arnold, Mudge, &c. See Longitude.

This appellation is now become common among artists, to distinguish such watches as are made with extraordinary care and accuracy for nautical or astronomical observations.

The principles of Mr. Harrison's Time-keeper, as they were communicated by himself, to the commissioners appointed to receive and publish the same in the year 1765, are as below:

“In this Time-keeper there is the greatest care taken to avoid friction, as much as can be, by the wheel moving on small pivots, and in ruby-holes, and high numbers in the wheels and pinions.

“The part which measures time goes but the eighth part of a minute without winding up; so that part is very simple, as this winding-up is performed at the wheel next to the balance-wheel; by which means there is always an equal force acting at that wheel, and all the rest of the work has no more to do in the measuring of time than the person that winds up once a day.

“There is a spring in the inside of the fusee, which I will call a secondary main spring. This spring is always kept stretched to a certain tension by the main spring; and during the time of winding-up the Time-keeper, at which time the main-spring is not suffered to act, this secondary-spring supplies its place.

“In common watches in general, the wheels have about one-third the dominion over the balance, that the balance-spring has; that is, if the power which the balance-spring has over the balance be called three, | that from the wheel is one: but in this my Time-keeper, the wheels have only about one-eightieth part of the power over the balance that the balance spring has; and it must be allowed, the less the wheels have to do with the balance, the better. The wheels in a common watch having this great dominion over the balance, they can, when the watch is wound up, and the balance at rest, set the watch a-going; but when my Timekeeper's balance is at rest, and the spring is wound up, the force of the wheels can no more set it a-going, than the wheels of a common regulator can, when the weight is wound-up, set the pendulum a-vibrating; nor will the force from the wheels move the balance when at rest, to a greater angle in proportion to the vibration that it is to fetch, than the force of the wheels of a common regulator can move the pendulum from the perpendicular, when it is at rest.

“My Time-keeper's balance is more than three times the weight of a large sized common watch balance, and three times its diameter; and a common watch balance goes through about six inches of space in a second, but mine goes through about twenty-four inches in that time: so that had my Time-keeper only these advantages over a common watch, a good performance might be expected from it. But my Timekeeper is not affected by the different degrees of heat and cold, nor agitation of the ship; and the force from the wheels is applied to the balance in such a manner, together with the shape of the balance-spring, and (if I may be allowed the term) an artificial cycloid, which acts at this spring; so that from these contrivances, let the balance vibrate more or less, all its vibrations are performed in the same time; and therefore if it go at all, it must go true. So that it is plain from this, that such a Time-keeper goes entirely from principle, and not from chance.”

We must refer those who may desire to see a minute account of the construction of Mr. Harrison's Timekeeper, to the publication by order of the commissioners of longitude.

We shall here subjoin a short view of the improvements in Mr. Harrison's watch, from the account presented to the board of longitude by Mr. Ludlam, one of the gentlemen to whom, by order of the commissioners, Mr. Harrison discovered and explained the principle upon which his Time-keeper is constructed. The defects in common watches which Mr. Harrison proposes to remedy, are chiefly these: 1. That the main spring acts not constantly with the same force upon the wheels, and through them upon the balance: 2. That the balance, either urged with an unequal force, or meeting with a different resistance from the air, or the oil, or the friction, vibrates through a greater or less arch: 3. That these unequal vibrations are not performed in equal times: and, 4. That the force of the balance-spring is altered by a change of heat.

To remedy the first defect, Mr. Harrison has contrived that his watch shall be moved by a very tender spring, which never unrolls itself more than one-eighth part of a turn, and acts upon the balance through one wheel only. But such a spring cannot keep the watch in motion a long time. He has, therefore, joined another, whose office is to wind up the first spring eight times in every minute, and which is itself wound up but once a day. To remedy the second defect, he uses a much stronger balance spring than in a common watch. For if the force of this spring upon the balance remains the same, whilst the force of the other varies, the errors arising from that variation will be the less, as the fixed force is the greater. But a stronger spring will require either a heavier or a larger balance. A heavier balance would have a greater friction. Mr. Harrison, therefore, increases the diameter of it. In a common watch it is under an inch, but in Mr. Harrison's two inches and two tenths. However, the methods already described only lessening the errors, and not removing them, Mr. Harrison uses two ways to make the times of the vibrations equal, though the arches may be unequal: one is to place a pin, so that the balance-spring pressing against it, has its force increased, but increased less when the variations are larger: the other to give the pallets such a shape, that the wheels press them with less advantage, when the vibrations are larger. To remedy the last defect, Mr. Harrison uses a bar compounded of two thin plates of brass and steel, about two inches in length, riveted in several places together, fastened at one end and having two pins at the other, between which the balance spring passes. If this bar be straight in temperate weather (brass changing its length by heat more than steel) the brass side becomes convex when it is heated, and the steel side when it is cold: and thus the pins lay hold of a different part of the spring in different degrees of heat, and lengthen or shorten it as the regulator does in a common watch.

The principles, on which Mr. Arnold's Time-keeper is constructed, are these: The balance is unconnected with the wheel work, except at the time it receives the impulse to make it continue its motion, which is only whilst it vibrates 10° out of 380° which is the whole vibration; and during this small interval it has little or no friction, but what is on the pivots, which work in ruby holes on diamonds. It has but one pallet, which is a plane surface formed out of a ruby, and has no oil on it. Watches of this construction, says Mr. Lyons, go whilst they are wound up; they keep the same rate of going in every position, and are not affected by the different forces of the spring; and the compensation for heat and cold is absolutely adjustable. Phipps's Voyage to the North Pole, p. 230. See LONGITUDE.

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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.

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THUNDER
THURSDAY
THUS
TIDES
TIERCE
* TIME
TISRI
TOISE
TONDIN
TONE
TONSTALL (Cuthbert)