Page:Cyclopaedia, Chambers - Volume 2.djvu/99

 LIG

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LIG

The Secret of inducing a Ligature is delivered by the fame Author,as he was taught it on the Spot by one of their Adepts ; which being a Curiofitv, we /hall not fcruple to add : Puella Amafium, vet Conjux matritum Ligaturus, ah- Jterget a Concubitus AElit, Priapum, lndttfio ut Seminis quan- tum potejl excipiet. Hoc probe convolution jub limine Domus Just in lerram fepeliai. Ibi quamdiu Jepultum reliquerit, tam- diu ejushafia in nultius praterqttam fui [fafcinantis) Servi- tium obediet, £5? prius ab noc h'exu non liberabitur quam ex claujlro liminis liberetiir ipfum linteum. Vice verfa, Vjr Lehli Socium Ligaturus, menjlruatum ab eo linteum comburito ; ex cineribus cum propria Urina fubaBis, efformato Figuram Pria- fi, vel ft Cineres latncuU ftngendd: non fufpeiant eofdem fub- igito cum Parte Terne quam recens perminxerit. Formatam Iconem cants exficcato, ficcamque afftrvato Loco flcco, ne Hu- morem contrahat. Quamdiu fie fervaverit, omnes Arcus dum ad Scopum Soci* collimaverint, momento contabefcent : Ipfe vero Dominus - ■ Abrunum hunc Juum prim bumeclato, quamdiu fie manebit, tamdiu fufpenfo nexu Priapus ipfi pa- rebit, quin & alios quotqttot Fxmina properantes admi- ferit.

M. Marjbal mentions another Form of Ligature which he received from a Bramine at lndojlan : * If, fays he,

' to two, and the one Part llirs, and the other not ; if the ' ftirring Part be bruii'ed and given with half a Beetle to ' a Man, and the other half to a Woman, the Charm will
 * the little Worm in the Wood Lukerara Kara be cut in-


 * keep each from ever having to do with any other Per-


 * fon.' PbtlofopbicalTranfaBions, Numb. 268.

Ligature;, among Printers, are Types confining of two Letters, or Characters which ferve to conneel two Letters together, as tf,jl,fi. The old Editions of the Greek Au- thors are extremely full of Ligatures 5 the Ligatures of Ste- phens are by much the moll beautiful. Some Editions have been lately printed without any Ligatures at all, and there was aDefign to explode them quite out of Printing. Had this fucceeded, the fineft antient Editions would in time have grown ufelefs, and the reading of old Manufcripts have been rendered almoft impracticable to the Learned themfeives.

LIGHT, a Term ufed in various Senfes : Sometimes it fignifies that Senfation occafioned in the Mind by the View of luminous Bodies; fometimes that Property in thofe Bodies, whereby they are fitted to excite thofe Senfations in us ; and, laftly, fome mean by it a certain Action of the luminous Body on the Medium, between that and the Eye, by means whereof they fuppofe the one to acl: on the other, and this they cssXX fecundary, or derived Light, to diftingui/b. it from that of luminous Bo- dies, which is called primary, or innate.

Arijlotle explains the Nature of Light, by fuppofing fome Bodies to be tranfparent, as Air, Water, Ice, &c. but fince in the Night-time we don't fee any thing thro' thofe Bodies, he fays, they are only tranfparent poten- tially ; whereas in the Day they become really and ac- tually tranfparent : and fince 'tis Light alone that can reduce that Power into Act, he defines Light to be the Acf of the tranfparent Body confidered as fuch ; «V J$ tstr w t»t« hvtpyuti t£ JJdpctySV h JiAe&v'u. He adds, that Light is not Fire, nor is it any thing bodily radiating from the luminous Body, and tranfmitted thro the tranfparent one ; but the mere Prefence of Fire, or fome other lu- minous Body at the tranfparent one. This is Arifiotle's Docfrine of Light, which his Followers miftaking, have foifted on him another, very different ; making Light and Colours to be Qualities of the luminous and colour'd Bo- dies themfeives, and in all refpecls like thofe Senfations which they occafion in us : adding, that Lucid or Co- lour'd could not produce any Senfations in us, unlefs they hadfomething fimilarin themfeives, fince nihil dat quod in fe non habet. But the Sophifm is apparent ; for wefind that a Needle in pricking the Flefh gives us Pain, which no body ever imagined to exift in the Needle. But that 'tis not neceffary there mould be any Similitude between the Quality of the Objefl, and the Senfation it produces, appears ftillmore evident from a Glafs Frifm, which is found to exhibite Blue, Yellow, Red, and other Colours extremely vivid, and yet nobo- dy will fay there is any thing in the Glafs Prifm like thofe Senfations.

The Cartefians have refined considerably on this Notion of Light, and own that Light, as it exifts in the luminous Body, isnothing elfe but a Power or Faculty of excitino in us a very clear and vivid Senfation ; adding, that what is required to the Perception of Light, is, that we be fo formed as to be capable of fuch Senfations, that in the hidden Fores of tranfparent Bodies there be a certain fub- tile Matter, which by reafon of its exceeding Smallnefs may penetrate even Glafs, and yet be ftrong enough to Ihake certain Capillaments at the bottom of the Eye ; and, laftly, that this Matter be impelled by the lumi- nous Body, fo as to move the Organ of Sight. Primary

Light thetefore, they fay, coniiils in a certain Motion of the Particles of the ' luminous Body, whereby they are enabled to propel every way the Materia Subtdis lodged in the Pores ot tranfparent Bodies, and fecundary or derived Light in a Conatus to Motion, or an Inclination of that Matter to recede from the Centre of the luminous Body in right Lines.

Father Malebrancb explains the Nature of Light, from a fuppofed Analogy between it and Sound ; the latter, 'tis allowed, is produced by the making or Vibrations of the infenfible Parts of the fonorous Body, which Vibra- tions, if they be greater or lefs, that is, if they run through greater or lefs Arches of the fame Circle, are ftill performed in the fame time, and the Sounds produced by them only differ in a greater or lefs Degree of Strength; but if there be a greater Number of Vibrations, in the fame time, in one fonorous Body than in another, thefe be ing clofer, become of a different kind : and thus their Sounds alfo differ, forming what we call different Tones or Notes ; the quick Vibrations forming the acute, and the flower the grave Notes. Thus he fuppofes it to be with Light and Colours. All the Parts of a luminous Body are in a very rapid Motion, which, by very quick Shakes, is conflantly comprefling the fubtle Matter between the lu- minou's Body and the Eye, and excites Vibrations of Fref- fion. As thefe Vibrations are more great, the Body ap- pears more luminous ; as they are more quick or more llow, the Body is of this or that Colour.

This Hypothefis, how ingenious foever, is now deferved- ly difcarded, fince rhe great Difcoveries made by Sir l/aac .IVmwob on this wonderful Phenomenon. The primary Light they talk of, we now know confifts wholly in a certain Mo- tion of the Particles of the lucid Body, whereby they don't propel any fiflitious Matter fuppofed to be lodged in the hidden Pores of tranfparent Bodies, but throw off, from the luminous Body, certain very fmall Particles, which areemit- ted every way with great force : And the fecundary or derived Light confifts, not in a Conatus, but a real Motion of thefe Particles receding every way from the luminous Body in right Lines, and with an' incredible Velocity. For if Light confifted in a mere Preffure or Fulfe, it would be propagated to all Diftances in the fame Inftant of Time ; the contrary of which appears from the Phenomena of the Eclipfes of Jupiter's Satellites, whofe Immerfions, as the Earth approaches towards Jupiter, are found to anti- cipate fomewhat on the true time, and to commence iooner ; and again as the Earth retires from Jupiter, their Emerfions, which alone in that Cafe can be obferved happen later and later, lofe time : deviating thus very confiderably on either fide, from the true time marked by the Tables. This was firft obferved by M Romer and fince by other Aftronomers ; the Reafon of which is not owing to any Eccentricity, but does apparently follow from 1 this, that the Light of the Sun reflcfled from the Satellites has further to travel, e'er it reaches the Eye in the one Cafe than in the other, by a Space equal to the Diameter of the Earth's annual Orbit Lhbt thetefore, like other real Bodies, does not move inftan- taneouily, but in Ttme. Sir Ifaac Newton has mewn pad contradiflion, that the Light of the Sun is near feven Minutes in its Paffage to the Earth, which is the Space of 50,000,000 Miles; a Velocity 10,000,000 Times greater than that wherewith a Ball flies out of the Mouth of a Cannon.

Further if i; g k W ere not a Body, but confifted in a

mere Preffure or Pulfion, it would never be propagated

m right Lines, but would be continually inflefled Vd

Umbram. Thus Sir Ifaac Nemon, ' A Preffure on a fluid

Medium f'-f; aMo tlo „ propagated b y fuch a Medium)

beyond any Obftacle which impedes any Part of its Mo

tion, cannot be propagated in right Lines, but will be

always infleamg and diffufin S itfelf every way to

the quiefcent Medium beyond that Obftacle. The

Power of Gravity tends downwards, but the Preffure of

Water r.fing from .trends every way with an equable

• £S*£r P r °P a g. ate n d Wfl equal Eafe and^qual Strength in Curves as in ftreighi Lines. Waves on the Surface of the Water, gliding y the Extreme's of a ^^'^ Obftacle, inflea/nd dilate themfel ves

ft rfu rP^y ™° 'he quiefcent Water be

• TthLlir wh ClC - J he F**»! ™ fa > or Vibrations < fluted L' T n So " nds ,™ fi ft> «e manifeftlyin-

Med tho notfo confiderab'y as the Waves of Wa- ter, and Sounds are propagated with equal Eafe thro- crooked lubes, and thro' ftrefht Lines but W™ never known to move in any Curve, nor to inflecf itfelf ad Umbram. The Rays of Ugh, therefore are fa Corpufcles emmed with exceding Celerity from tU luminous Body As ,0 the Force wherewith thefeCor pufcles are emitted, foas toemble them to move a, he inconceivable Rate of 7,000,000 Miles in a Minute hear the fame great Author; • A»ong Bodies of the' fame

' Kind