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oxygen; that he had succeeded in ob- and galvanic agents. See Murray's Che.
. mated by Dr. Thomson at 38, is in a very Its colours are numerous, blue, green, short space of time considerably reduced. red, of numerous shades, and yellow or Chemistry, indeed, as a science, will yellowish white, and sometimes more than probably undergo a complete renovation: one colour is present even in the same the discoveries of Mr. Davy promise a crystal. It is more or less transparent; total overthrow to the beautiful, and, as its lustre is resplendent and vitreous; it was formerly deemed, simple, and al- and it often presents a beautiful reflection most perfect system of Lavoisier. The of light, in the form of a star: the fracture English professor assumes electricity as a is conchoidal, or imperfectly foliated; the general agent of decomposition; that dif- hardness is inferior to that of the dia. ferent bodies are naturally in different mond, but superior to that of every other electrical states; that by altering these fossil, and not yielding to the file: the states their affinities are altered. In justi. specific gravity is from 3.9 to 4.1. fication of this theory, he has ascertained TIME, equation of. The most usual and that oxygen, and all bodies containing an best measure of time that we have is a excess of oxygen, are naturally negative, clock, regulated by the vibration of a pen. and that all bodies containing an excess dulum. But with whatever accuracy a of inflammable principle are naturally clock may be made, it must be subject to positive. Should subsequent facts con- irregularities, as well from the imperfecfirm this theory, it is highly probable that tion of the workmanship, as from the many other of the bodies, hitherto regard. expansion and contraction of the materied as simple, will yield to the powers of als by heat and cold, by which the length his apparatus.
of the pendulum, and consequently the SUBSTANCES, imponderable, in chemistry, time of vibration, will vary. As no clock, are, caloric, light, electricity, and galva- therefore, can be depended upon for nism; perhaps the identity of the two keeping time accurately, it is necessary former may bereafter be discovered : and that we should be able at any time to as. likewise that of the two latter more com certain how much it is too fast or too slow, pletely demonstrated. The common cha- and at what rate it gains or loses. For racter that they all possess is, that of this purpose it must be compared with not being subject to the attraction of some motion which is uniform, or of gravitation; at least their gravity has which, if it be not uniform, one can find hitherto been incapable of appreciation, the variation. The motions of the hea. hence the term “imponderable.” They venly bodies have therefore been consi. possess the greatest subtility, or tenuity; dered as most proper for the purpose. they cannot easily be obtained in a sepa. Now as the earth' revolves uniformly rate state of existence; they are observed about its axis, the apparent diurnal mo. only in states of combination, or in their tion of the heavenly bodies about the axis rapid transition from one body to another. must be uniform. If a clock, therefore, We can scarcely discover their specific he adjusted to go 24 hours from the pasaffinities, or measure their force, and we sage of any fixed star over the meridian are unable to trace their particular com till it returns to it again, its rate of going binations, or consider them as essential may be determined by comparing it with constituent
principles of any compound. the transit of any fixed star, and observing They are moreover diffused over every wherher the interval continues to be 24 kind of matter; at least caloric exists in hours: if not, the difference shows how all bodies, and probably also the electric much it gains or loses in that time. A
clock thus adjusted is said to be adjusted time from the passage of a fixed star over to sidereal time, and all the sidereal days the meridian till it returns to it again. are equal. But all the solar days are not From these considerations it will be evi. equal, that is, the intervals from the sun's dent, that if a clock be adjusted to go 24 leaving the meridian till it returns to it hours in a mean solar day, it will not conagain are not all equal; so that if a clock tinue to coincide with the sun, that is, to be adjusted to go 24 hours in one interval, show 12 when the sun comes to the meri. another interval will be performed in dian, because the true solar days differ in more or less than 24 hours, and thus the length from a mean solar day; but the sun and the clock will not agree; that is, sun will pass the meridian, sometimes be. the clock will not continue to show 12 fore 12, and sometimes after 12, and this when the sun comes to the meridian. It difference is called the equation. A clock is found that the length of the solar day thus adjusted, is said to be adjusted to is equal to the time of the earth's rotation mean solar time. The time shown by the about its axis, together with the time of clock is called true or mean time; and describing an angle equal to the increase that shown by the sun is called apparent of the sun's right ascension in a true solar time: thus, when the sun comes to the day. Now if the sun moved, or appeared meridian, it is said to be 12 o'clock appato move, uniformly, and in the equator, rent time. Hence the time shown by the this increase would be always the same in sun-dial is apparent time; and therefore a the same time, and therefore the solar days dial will differ from a clock by how much would be all equal; but the sun moves, or the equation of time is on that day. appears to move, in the ecliptic; and, When, therefore, we set a clock or watch therefore, if its motions were uniform, by the dial, we must attend to what the equal arcs upon the ecliptic would not equation of time is upon that day by a tagive equal arcs upon the equator. But ble, such as that given below, and allow the apparent motion of the sun in the for it: thus, if the equation be 4 minutes, ecliptic is not uniform, and hence also as it is on new year's day, and the watch any arc upon the ecliptic, described in a or clock be faster than the sun ; then the given time, is subject to a variation, and watch or clock must be made to show 4 consequently that on the equator is sub. minutes past 12 when the dial shows 12 ject to a variation. The increase then of precisely. On the 30th of April, when the the sun's right ascension in a true solar dial shows 12, the clock or watch, to be day varies, from two causes : first, because accurate, must want 3 mintes of that the ecliptic, in which the sun appears to hour, and so of the rest. In calculating move, isinclined to the equator; secondly, tables of the equation of time, for every because his motion in the ecliptic is not day in the year, the sun and clock are set uniform, therefore the length of a true together, when the sun is in bis apogee, solar day is subject to a continual variation; and then they investigate the difference consequently, a clock which is adjusted to between the sun and the clock, for every go 24 hours for any one true solar day, day at noon, and insert them in a table, will not continue to show 12 when the stating, by means of the signs + and , sun comes to the meridian, because the how much the clock is before or afterthe intervals by the clock will continue equal, The inclination of the equator to if the clock be supposed accurate ; but the the ecliptic, upon which the equation of intervals of the sun's apparent passage time partly depends, and the place of the over the meridian are not equal.
sun's apogee, when the clock and sun set As the sun appears to move through off together, being both subject to vary, 360° of right ascension in about 3654 days, the equation of time for the same days of therefore 365.25 : 1 day :: 360° : 59 gói the year will every year vary, and there2", the increase of right ascension in one fore it must, where great accuracy is reday, if the increase were uniform; or it quired, be calculated for every year. Bewould be the increase in a mean solar sides the time when the sun is in his apo. day, that is, if the solar days were all gee, there are three other times of the equal; for they would be all equal, year when the clock and sun agree, or if the sun's right ascension increased uni when mean and apparent time is the same, formly. As the earth describes an angle as will be seen in the following table, of 360° 59', about its axis in a mean so which is adapted to the second year aflar day of 24 hours, and an angle of 360° ter Bissextile, and will always be found in a sidereal day, we say, as 360° 59 8' 2": within a few seconds of the truth, and, 360° :: 24b : 23h 56' 4", the length of a therefore, sufficiently accurate for all sidereal day in mean solar time, or the common purposes.
TABLE FOR THE EQUATION OF TIME.
3 5 7 9 12 15 18 21 25
31 Feb. 10
27 Mar. 4
8 12 15 19 22 25 28
4 +|| April 1
May 13 14
29 15 June 5 14
29 8 July 5 7
4+ || Aug. 9
Oct. 3 4
1 2 3 4 5 6 7 8 9
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
16 18 20 22 24
TRIGONOMETRY. Some of the re tres Poloni. In the fifth page, for similar, ferences to the figures are not quite cor- read nearly similar. rect, but the figures speaking so plainly for themselves, a more particular correc Such, it is believed, are the chief errors tion is deemed unnecessary
and omissions : others, of less importance, UNITARIANS. In the third ge of the candid and liberal reader will excuse, this article, for Polones Fratres, read Fra- and will readily correct for himself.