Page:Cyclopaedia, Chambers - Volume 2.djvu/695

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eUes a different Explication. In ettect, all that has hitherto been advanced on this Point, is mere Conjec-
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SECANT, in Geometry, a Line that cuts another, or „.vides it into Two Parrs: Thus the Line AM. (lab. Geometry Fig. n) is a Secant of the Circle AEU, iyc. as it cuts the Circle B. 'T, S demonllrated by Geometers; ,° That if l'everal Secants MA, MN, ME, i£c- be drawn from the lame Point M, that pafling through the Centre M A, is the greateft, and the reft are all lo much the lets, as they are more remote from the Centre. Un the contrary, the Portions thereof without the Circle MD MO, MB, are ib much the greater as they are further from the Centre. The leaft, is that of M A, which paffes through the Centre. 2° That if Two iWlM A and M E, be drawn from the fame Point M ; the Secant M A, will be to ME as MD to M B. See Tangent.

Secant, in Trigonometry, a right Line, drawn from the Centre of a Circle, which cutting the Circumference, proceeds, till it meets with a Tangent, to the fame Circle. Thus the Line FC (Tab. Trigonometry Fig lO. drawn from the Centre C, till it meet the Tangent E F, is call d a Secant, and particularly the Secant of the Arch A E, to which F E is a Tangent. The Secant of the Arch A H, which is the Complement of the former Arch to a Quadrant, is call'd the Co-Secant, or Secant of the Com- pteuieut.

The Sine of an Arch AD, being given; To find the Secant thereof FC, the Rule is, As the Co fine ADC is to the Sine A D, lb is the whole Sine E C, to the Secant C F.

To find the Logarithm of the Secant of any Arch : The Sine of the Complement of the Arch being given ; multiply the whole Sine of the Logarithm by Two, and from riie Product lubtra£l the Logarithm of the Sine Complement, the Remainder is the Logarithm of the Secant. See Logarithm.

Line of Secants. SeeSECTort.

SECOND in Anatomy. See Secdndi Generis.

Seconp in Geometry, Ajironomy, Stc. the Sixtieth Part ot a Prime or Minute; either in the Divifion ol Cir- cles, or in the Meafute of Time. A Degree, or an Hour, are each divided into 60 Minutes, marked thus ' : A Minute is tubdivided into 60 Seconds, marked thus"; a Second into 60 Thirds, marked thus '", £i?c. See Degree. We fotnetimes lay a Second Minute, a Third Minute, lie but more uliially, Amply Second,Third, lie. A Pendulum Three Feet Three inches, and two Tenths of an Inch long, vibrate's Seconds: According to Sir Jonas Moor's Reduction of Hmgen'i Three Feet Eight Lines and an Halt of 'Paris Meafure, to Englip Meafute. See Pen- dulum.

Second in Mufick, one 6f the mufical Intervals ; being only the Dillance between any Sound, and the next nearell Sound ; whether higher or lqwer. See In- terval. As in the Compafs of a Tone, there are reckoned Nine fenfiblc, different Sounds, which form thole little Intervals, call'd Commas ; one might, in ftricV nels, fay, there are Eight kinds of Seconds. But as thefe minute Intervals, though lenfible, arc not yet lb far lb, as to contribute much to the Harmony, rhey uliially only dillioguifh four Sorts. The Firft called, The diminijli'd Second, containing Four Commas, and is the Diffe- rence, for Inllance of a natural ut, and an at railed four Commas higher. The Second, call d Second Minor, contains Five Commas, and is made either naturally, as From mi to fa, or from ft to ut; or accidentally, by means of b, as from ta to ft, bflat; or from fa diefis to fol; otherwife called a Major Semitone, or imperfect Second, or Italian Semitone. The Third is the Major Second, containing the Nine Commas, which compoie the Tone. This the Italians call Tono or perfect Second. The Fourth is rhe Second Redundant, compofed of a whole Tone and a minor Semitone.

Second Terms, in Algebra, thofe where the un. known Quantity has a Degree lefs than it has in the Term where 'tis rais'd to the higheft. The Art of throw- in" rhcie Second Terms out of an Equation; that is, of forming a new Equation, where they have no Place, is one of the molt ingenious and uieful Inventions in all Algebra. See Reduction of Equations.

Second Captain, is a reform'd Captain, who airs as Lieurenant of another, into whofe Company he is In- corporated. See Captain.

Second Caufe. See Cause; and Efficient.

Second Sight, an odd Qualification, many of the Inhabitants of the Weftern [Hands of Scotland are (aid to be poffefs'd of. We have the Thing fo well arreted, by fo many credible Authors (the latcltof whom is Mr Ajar- tin, the Ingenious Author of the natural Hiftory of thefe

Iflands, and a Member of the Royal Society) that, notwith- Handing the Quaintnels oi the Thing, there is fcarce Room to call it in Queftion. The Second Sight, is a Facuhyot" feeing Things to come, or Things doing at a great Di_ fiance, reprelented to the Imagination as if a&uallv vifible and prelenr. Thus if a Man be dying, or about to die, his Image fhall appear diftinftly in its natural Shape, in a Shroud, and with other funeral Apparatus to a Second Sighted Peribn, who, perhaps, never fa w his Face before: Immediately after which, the Peribn ibfeen certainly dies. This Quality uf Second Sigl'tednefs, is not ' hereditary : The Perlon who has it, cannot exert it Jt pleafure ; nor can he prevenr it, or communicate it to another ; but it comes on him involuntarily, and exerciies irielf on him arbitrarily. And of.en, elpecially in the younger Second Seers, to their great Trouble and Terror. There are a great Number of Circumltances attend thele Virions, by Oblervation whereof, the particular Circum- flances as to Time, Place, &c. of rhe Death of the Per- ibn, are learnt. The Method of judging of them, or in- terpreting them, grows into a kind of Art ; which is very different in different Pcrfons. Second Sgbtednefs, is held a Diicredit among them ; fo that none will counterfeit it ■ manv conceal and diffemble it.

SECONDARY Circles, in reference to the Ecliptick, or Circles of Longitude of the Stars, are liich, as paifing rhrough the Poies ot the Ecliptick, are ar right Angles to the Ecliptick (as the Mendian and Hour Circles are to the Equinoctial). By me Help of thefe, all Points in the Heavens are referred to the Ecliptick ; that is, any Star, Planer or orher Phenomenon, is underflood to be in that Point of the Ecliptick, which is cut by the Secondary Semicitcle, which paffes through fuch Star or Phenome- non: And if two Stars are th';* reterr d to the lame Point of the Ecliptick, they are laid to be in Conjunction ; if in oppofite Points, they are faid to be in O, poiition: If they are referred to two Poinis at a Quadrant sD.itaiice, they are faid to be in a Quarrile Aipect ; if the Points differ a fixth Part of rhe Ecliptick, they are faid ro be in a Sextile Afpecf. And in general, all Circies which in- teract one of rhe Six grearer Circles of rhe Sphere at Right Angles, maybe called Secondary Circles ; as the Azimuth or Verrical Circles in relpect of the Horizon,

efe. , ,..

Secondary Fever, is that which arifes after a Crifis, or theDifcharge of fnme morbid Matter, as after the Dedenfion of the Small Pox, or Meaflesj and fuch a Fever is frequently dangerous. See Fever.

Secondary ^Planets, thofe moving round other ^Planets, as the Centres of their Motion, and along with them round the Sun. See Planet.

Saturn, Jupiter, and the Earth, are each attended with Secondary 'Planets: Jupiter with four, and Saturn with five, called the Satellites of thole two Planets* See Satellites. The Bart/3 with one called the Moon. See Moon.

The Motion of the Trimary Planets, is very fimple and uniform, as being compounded only of a Proje&ile Morion, forward in a right Line, which is a Tangent to the Orbit, and a Gravitation towards the Sun at the Centre, Add, That being at fuch vaft Diftances from each other, the Effe&s of their mutual Gravitation towards one ano- ther are infenfible : But the Matter is far otherwife, in refpedl of the Secondary 'Planets $ for every one of thefe, though it chiefly gravitate towards its refpe&ive Prima- ry One, as towards its Centre, yet at equal Diftances from the Sun, is attracted towards him with equally acce- lerated Gravity, as the primary One is towards him, but at a greater Difiance with left, at a nearer Diftance with greater; from which double Tendency towards the Sun, and towards its own Primary Planet, the Motion of the Satellites, or Secondary 'Planets, comes to be mightily compounded, and affected, with many Inequalities : As for lnftance, (i.) The Satellite fhall be continually acce- lerated in its Motion, from the Time of its Quadrature with the Sun, to the next following Conjunction or Op- position j but contrary-wife from the Syzygies to the Quadratures, it fhall be retarded, and therefore will not always move fwifter in or near the Syzygies, and flower near the Quadratures. From whence will follow, (2.) That the Orbits of thele Secondary 'Planets, will be of a Figure more Circular in the Quadratures than in the Syzygies, where the Swiftnefs of the Motion will make the Figure of the Orbit more Rectilinear, and therefore the Satellite will run farther from its Primary Planet at the Quadra- tures, than at the Syzygies, io that the Orbit wilT be a little elliptical, having the primary Planet for its Centre, artd fhe longer Diameter will coincide with the Line of the Quadratures, and the fhorter with that of the Syzy- gies. Which Irregularities will arife, if the Sun's Power of perturbing the Motion qf the Satellite be ex- cluded, and the Orbit be coiteentrick wish that of the

Primary