IS
new iflands formed^ by the carting up of vaft Heaps of Clay, Mud, Sand, £gc. as that for inftance of Tfong- . mingy in the Province of Tunquin in China : or by the Vio- lence of the Sea, which have torn off large Promontories from the Continent, as the Antients imagined Sicily, and even Great Britain were formed. It is alio certain, that fome have emerged above the Waves, as Santorini former- ly, and three other Hies near it lately j the lall in i 707, which rofe from the bottom of the Sea after an Earth- quake, that was fuppos'd to have loofen'd it from its hold.
Several Naturaliits are of opinion, that the [[lands were formed at the Deluge 5 others think they have been fe- parated from the Continent by violent Storms, Inunda- tions, and Earthquakes. Thefe laft have obferved, that the Baft-Indies, which abound in Iflands more than any o- ther part of the World, are like wife more annoyed with Earthquakes, Tempefls, Lightning, Vulcano's, &c. than any other Part. Varenms thinks moll of thefe Opinions true in fome -Inftances, and believes that there have been Iflands produced each of thefe ways. St. Helena, Jf- cenfion, and other fteep rocky Mono's, he fuppofes to have become fo, by the Sea's overflowing their neighbouring Champains. By the heaping up huge Quantities of Sand, and other terrellrial Matters, he thinks the Iflands of Zea- land, *3afan, Sic. were form'd. Sumatra and Ceylon, and mod of the Baft-Indian Ifimds he thinks were rent off from the main Land ; and concludes, that the J '/lands of the^r- chifehgo were form'd in the fame way ; imagining it probable, thatDsHw/io«'s Flood might contribute towards it. The Antients had a Notion, that Betas, and fome/ew other Iflands, rofe from the bottom of the Sea. Which, how fabulous foever it may appear, agrees with later Obferva- tions. Seneca takes notice that the J (land Thcrafia rofe thus out of the JEgean Sea in his time, of which the Mariners ■were Eye-wirnefles. They had alio an opinion, that there are fome Iflands which fwira in the Sea. Thales, indeed, thought that the whole Earth which we inhabit, floated, thus, in the Sea ; but his Opinion is cafily refuted, the Channel of the Sea being found continuous to the Shore : But floating Iflands are no ways improbable, efpecially if the Earth whereof they confiit be light and fulphureous. Senecafays, that near the CutylU he law fuch anlfland, and mentions feveral others of the fame kind ; and it was even a common Opinion among the Antients, that all the Cy- clades had done the fame. Gryfhiandtr has written a Latin Treatife exprefly on Iflands, de Infulis.
ISLES, in Architecture, are Sides or Wings of a Build- ing.
ISOCHRONAL LINE, is that in which a heavy Bo- dy is fuppofed to defcend without any Acceleration. Leib- nitz in the AB. Erud. Liff. for February 1689, hath a Dif- courfe on this Subject, in which he ihews, That a heavy Body with a degree of Velocity acquired by the De- fcent from any Height, may defcend from the fame Point, by an infinite Number of ifoohronal Curves which are all of the fame Species, differing from one another only in the Magnitude of their Parameters, fuch as are all the Quadrato-Cubical Paraboloids, and confequently fimi- lar to one another. He /hews alio, there, how to find a Line, in which a heavy Body defcending mall recede uni- formly from a given Point, or approach uniformly to it.
ISOCHRONE b a Term applied to fuch Vibrations of a Pendulum as are performed in equal Times : of which kind are all the Vibrations or Springs of the fame Pendu- lum, whether the Arcs it defcribes be longer or ihorter 5 for when it defcribes a ihorter Arc, it moves fo much the flower; and when along one, proportionably fafter.
ISOMERIA, in Algebra, is a Method of freeing an E- quation from Fractions, which is done by reducing all the Iradions to one common Denominator, and then multi- plying each Member of the Equation by that common
Denominator. Thus e. g. |.\»-f-fl x x =ss a b h be-
a comes ax* -\-$aax x — ^bcx = 4aabb.
ISOPERIMETRAL FIGURES, are fuch as have c- qual Perimeters or Circumferences.
ISOSCELES Triangle, is a Triangle which hath two equal fides 5 to which it may be added, that the Angles oppofite to the equal Sides are e- qual, and a Line drawn from the Top or Vertex, cutting the Bafe into two equal Parts, is perpendicu- lar to the Bafe . e.%. Let the Ifofceles Triangle be A P C, and let its Bafe A C be fuppofed to be divided into two equal Parts in m : } fay, P „ j s perpendicular to A C, and the Angle P C A is equal to the Angle P A C 5
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for the Triangle Z hath all its Sides equal to thofe of j£ and therefore mult have all its Angles equal olfo refpec lively to thofe m X : And then the Angle P m i = f» C, becauic they are both right ; therefore P „ j s perpendicu- lar to A C, and the Angle P A m = P Cm.
ISSUANT, a Term in Heraldry, undcrilood of a Lion, or other Animal, ma Coat of Arms, that fcems juft iffu- ing out from under a Chief, Feffe, a Houfe, a Wood, or ?S. llke ;, ai ' d onl y /llews hll f his Body. It is not cafy to ciiftmguiih the Lion Iffjtant from the Lion Naiffam. Some lay the Iffuasitts that which comes out from behind the field of fome ample Ordinary, /hewing his Head, Neck, the 1 ips of his Fore-Legs and his Tail againft the chief of the Coat 5 whereas the Naiffant has its Rife about the middle of the Field, and mews all his Fore-part, with the Tip of his Tail, as if he were riling out of the Earth.
ISSUE, is a Term in Common Law, hiving divers Ap- plications j fometimes it is taken for the Children begot- ten between a Man and his Wife; fometimes for Profits growing from Amerciaments or Fines ; and fometimes from Profits of Lands and Tenements; fometimes for that Point of Matter depending in Suit, whereupon the I arties join, and put their Caufe to the Tryal of the Ju- ry : And yet in all thefe it hath but one Signification which is an Effect of a Caufe preceding ; as the Chil- dren are the Effect of the Marriage between the Parents : The Profits growing to the King or Lord, from the Pu- mfhment of any Man's Offence, is the Effect of his Tranf- greffion : The Point referred to the Tryal of twelve Men, is the Effect of Pleading or Procefs. lffue, in this kit Sig- nification, is either General or Special.
General Ijite feemeth to be that whereby it is referred to the Jury to bring in their Verdifl, whether the Defen- dant hath done any fuch thing as the Plaintiff lays to his charge : For example, If it be an Offence againft any Statute, and the Defendant plead Not Guilty ; this beinf put to the Jury, is call'd the General lffue. And if a Man complain of a private Wrong, which' the Defendant de- nieth, and pleads no Wrong, 'nor Diffeifin ; and if this be referred to the Jury, it is likewife the General IJfue.
The Special IJfue then mult be that, when Special Mat- ters being alledged by the Defendant in his Defence, both Parties join thereupon, and fo grow rather to a Demurrer, if it be Quxfiit 'Juris ; or to a Tryal by the Jury, if it be Quxftio FaBi. '
ISSUES, in Phytic, are fmall artificial Apertures in a fle/hy part of the Body, to drain sff fuperfluous Moilture, or give vent to any noxious Humour. They are ulually made in the Arms, Legs, or Back, either by Cauftics or Incifion. Caution is ufed to place them about the middle of aMufcle, that the neceffary Motion of the Parts may not incommode them, or pain the Patient. There is an ' eafy way of making an lffue, which fucceeds bell in Chil- dren ; 'tis done after this manner : Having applied a fmall piece of buffering Plailtcr, about the bignefs of a fmall Pea, to the Part where you would have an lffue, and letting it lie on for a few Hours, it will caufe a Bliiler; the Skin being rais'd, apply a Pea as ufual, and com- prefs it tight with a Bandage, till by degrees it finks in, and forms an lffue. Iffues are very ufeful in many Diltem- pers, feveral of which, when obffinate, cannot be cured without them ; as an Hydrocephalus, Optbalmia, Old Ul- cers, Sic.
ISTHMUS, a narrow Neck or Slip of Ground that joins two Continents, or joins a Cherfonefus or Pcninfula-to the Terra jirma ; and feparates two Seas. The molt cele- brated Ifthmus's are thofe of Panama or Darien, which joins North and South America ; that of Suez, which con- nects Afia and Africa ; that of Corinth, or Pelofannefus, in the Morea ; that of Crim-Tartary, otherwife called the Tau- rica Cherfonefus ; that near the Ifland of Romania and Eriffo, or the Ijihmus of the Thracian Cherfonefus, twelve Furlo'n«s broad ; being that which Xerxes undertook to cut through. The Antients had feveral Defigns of cutting the Ifthmtisoi Corinth, which is a rocky Hillock, about ten Miles over ; but they were all vain, the Invention of Sluices being not then known. There have been Attempts, too, for catling the Iftbmus of Suez, to make a Communication between the Red-Sea and the Mediterranean. The word comes from the Greek i&iilf, a Nech Hence Anatomifls trie the Term. for feveral Parts of the human Body, particularly that narrow part of the Throat fituate betwixt the two Ton- fils ; and the Ridge that feparates the two Noftrils.
ISTHMIAN GAMES were facred Sports, the third, in order, of thofe fo much celebrated in antient Greece'. Plutarch, in the Life of Thefeus, tells us, they were infti- tuted by that Hero in imitation of Hercules, who had be- fore inlliruted the Olympian Games; but Archias refers their Inititution to Melicerta or Pai.tmon, whom the Latins call Portunus. Others fay they were inftituted by Nijls, Son of Neptune; and oihers by Sifypbts, Brother of Aiha-
