T I M 



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T I M 



recapitulation always says that time has passed quickly, 

 another of a contrary habit the contrary ; and this whether 

 the rapidity is a consequence of quickness of ideas, or ol 

 having little to recall. 



In all the more correct machines which have been in- 

 vented to measure time, there is but one principle : a vi- 

 bration is kept up by the constant application of forces 

 only just sufficient to counteract friction and other resist- 

 ances, and machinery is applied to register the number 

 of vibrations. The remarkable law noted under ISOCHRO- 

 NISM and VIBRATION makes it comparatively immaterial 

 whether the vibrations are of precisely the same extent. 

 But the imperfections of such instruments, or rather, our 

 ignorance of the precise action of disturbing causes, and 

 particularly of changes of temperature, renders them com- 

 paratively useless for measuring long periods, so that if we 

 could not have recourse to the motion of the heavenly 

 bodies, there would be no permanent measure of time. 

 And even in astronomical phenomena there is no absolute 

 recurrence at equal intervals, though nearly enough for 

 common purposes. The value of such phenomena for the 

 most accurate measures consists in most of their irregulari- 

 ties being truly distributed about a uniform mean, so that 

 the excesses of some periods are compensated by the de- 

 fects of others, giving, in the long run, power of determin- 

 ing that mean with as much accuracy as our modes of mea- 

 surement can appreciate. The determination of time for 

 civil reckoning may be divided into two parts : first, the 

 mode of making the different periods derived from the sun 

 and moon agree with each other so as to afford an easy 

 method of reckoning co-ordinately by both [PERIODS OF 

 REVOLUTION] : secondly, the mode of procuring true and 

 convenient subdivisions of the natural unit consisting of a 

 day and night. To the second of these we now turn our 

 attention. 



The actual revolution of the earth, as measured by the 

 time elapsed between two transits of the same star over the 

 meridian, is called a sidereal day. It is divided, as are all 

 other days, into twenty-four hours of sixty minutes each, 

 &c. The time so given is called sidereal time. If the sun 

 were a fixed star, this sidereal time would be the common 

 mode of reckoning. But the sun having its own slow 

 motion in the ecliptic, in the same direction as the revolu- 

 tion of the earth, the interval between one meridian transit 

 of that body and the next is [SYNODIC] longer than the 

 simple revolution of the earth, for just, the same reason 

 that the time which the minute-hand of a watch moves 

 from coincidence with the hour-hand to coincidence again 

 is longer than the hour, or simple revolution of the minute- 

 hand. If the sun moved uniformly, and in the equator, 

 the real solar day, which means the interval between two 

 meridian transits of the sun, would always be of the same 

 length, and a little longer than the sidereal day. But the 

 gun neither does move uniformly, nor in the equator ; and 

 each of these circumstances causes a slight irregularity in 

 the absolute length of the solar day, or, as it is called, the 

 real solar day. This is the reason why the time shown by 

 a sundial does not agree with the watch. To remedy this 

 inconvenience, a fictitious sun is supposed to move in the 

 ecliptic, and uniformly, while another fictitious sun moves 

 in the equator, also uniformly. Both the fictitious bodies 

 have the average motion of the real sun, so that the years 

 of the three are the same; and the fictitious sun of the 

 ecliptic is made to coincide with the real sun at the perigee 

 and apogee, or nearest and farthest points from the earth ; 

 while the fictitious body in the equator is made to coin- 

 cide with the fictitious body of the ecliptic at the equinoxes 

 (from which it arises that there is also a coincidence at the 

 solstices). This fictitious sun of the equator is that to which 

 clocks are adjusted ; the interval between two of its transits, 

 which is always of the same length, is called a mean solar 

 day, which is divided into twenty-four mean solar hours, &cc. 

 The difference between time as shown by the real sun and 

 the fictitious sun in the equator, is called the equation of 

 time. 



The determination of the equation of time is a mathe- 

 matical problem of some complexity : what we have here 

 to notice is, that owing to the joint action of the two 

 sources of difference, it presents a very ii-egular series of 

 phenomena in the course of the year. If the sun moved 

 regularly, but in the ecliptic, there would be no equation 

 lit' time at the equinoxes and solstices : if the sun moved 

 with its elliptic irregularity, but in the equator instead of 



the ecliptic, there would be no equation of time at the 

 apogee and perigee. Between the two the equation of 

 time vanishes only when the effect of one cause of irregu- 

 larity is equal and opposite to that of the other ; and this 

 takes place four times a year. In this present year (1842) 

 the state of the equation of time is as follows : January 

 1, the clock is before the sundial 3 m 51 s , and continues to 

 gain upon the dial until February 11, when there is 

 14 m 35 s of difference. This then begins to diminish, and 

 continues diminishing until April 15, when the two agree, 

 and there is no equation. The dial then is before the 

 clock until May 14, when the equation is 3 m 55s, which 

 diminishes until June 15, when there is again no equation. 

 The clock is now before the dial, and the equation increases 

 till July 26, when the equation is 6 m 10 s , which diminishes 

 until the 1st of September, when there is no equation, for 

 the third time. The dial is now again before the clock j 

 and by November 2 the equation has become 16 m 18 s , from 

 which time it falls off until December 24, when it is 

 nothing for the fourth and last time. The clock then gets 

 gradually before the dial till the end of the year. The 

 phenomena of the next year present a repetition of the 

 same circumstances, with some trivial variations of mag- 

 nitude. There are several slight disturbing causes fa 

 which we have not thought it worth while to advert in a 

 popular explanation : in particular, the slow motion of the 

 solar perigee [YEAR; SUN], which will in time wholly 

 alter the phenomena. For instance, when the perigee 

 comes to coincide with the equinox, there will be only two 

 periods at which the equation of time vanishes, namely, 

 when the sun is at either equinox. 



The sidereal day is 23'> 5C m 4 s . 09 of a mean solar day, 

 and the mean solar day is 24'> 3 m 56 s . 55 of a sidereal day. 

 We have in this article only to do with the mode of obtain- 

 ing a uniform measure of time, or of intervals of time ; this* 

 being premised, the subject will be taken up again in the 

 article YEAR. 



TIME BARGAIN. [STOCKS.] 



TIME OF DESCENT, the technical term for the time 

 employed by a material particle in falling down an arc of 

 a curve under the action of gravity, the mode of obtaining 

 which is explained in VELOCITY. When any number of 

 curves are drawn from a given point, and another curve isi 

 so drawn as to cut off from every one of them an are whichi 

 is described by a falling particle in one given time, that 

 curve is called tautochronous, or a tautocttron. But when 

 a curve is such as the cycloid, namely, that a particle, 

 wherever placed, will fall to the lowest point in the same 

 time, such a curve is also called tautochruiinus by various 

 writers, and isochronous by others. Our only object in. 

 inserting this article has been to note this confusion of 

 language. 



TIME (in Music) is : 



I. The measure of the duration of sound. 



II. That which divides a bar into two or three equal/ 

 parts, and subdivides these. 



III. The movement i.e. the quickness or slowness of 

 a composition. 



1. The degree of sound, or pitch, is shown by the place 1 

 on the staff of any one of the characters called notes ; but 

 its duration is known by the particular note ; that is, as 

 minim, or crotchet, &c. The longest note, in relation to: 

 time, used in modern music, is the senlibrevc, which is 

 considered the measure-note, and its average length is 

 about four beats of a healthy man's pnlse. The five other- 

 notes are proportionate parts of this. Thus the minim is. 

 in duration of a semibreve ; the crotchet is , &e. : con- 

 sequently two minims, or four crotchets, &c., are equal to> 

 one semibreve, as exhibited in the annexed table : 



