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way of Legitimation by the Emperor's Letters. This ren- dered Baf lards capable of attaining to Honours, and even of fucceeding to Inheritances, provided the Perfons were legitimated with the Confcnt of their Father and Mother ; which is agreeable to the Canon Law.
LEGS, the lower Parts of the Bodies of Animals, ferving them for Support and for Motion. Some Anato- mitts divide the Foot of Man into three Farts, -viz. the Thigh, the Leg, and the lcffer Foot. In the Leg there are two confiderable Bones, the one called The Great Fa- cile, or the Tibia ; the other The Little Facile, or the Fibula.
TheLegsa.nd Feet of the feveral Animals, Nit.Derham obferves, are exactly conformable to the Pofture, Make, nay to the Motion and Exercifes of thofe Animals. In fome they are made for Strength only, in others for Agili- ty and Swiftnefs ; in fome for walking and running, in others for fwimming, in others for digging, and in others for flying. In fome more lax and weak tor traverfing the plain Land, in others ftifF and rigid for Ice and Precipices. In fome ihod with tough and hard Hoofs, fome whole, fome cleft. In fome the Feet are compofed of Toes, fome fhort for only going, others long to fupply the Place of Hands 5 fome armed with Talons to catch and tear their Prey, fome with fhort Nails to confirm their Steps in running and walking. In Birds the Legs are curved for their cafy Perching, Rooming, and Reft, as alio to help them on the Wing in taking their Flight, and tobethereincom modioufly tucked up to the Body,fo as not to obftruct their Flight. In fome long for wading, &c.
Legs of a Triangle j when one Side of a Triangle is ta- ken as a Bafe, the other two are called Legs,
LEGUMEN, in Botany, is [that Species of Piants called Fulje j which are fo named as being gathered with the Hand, by which they are diftinguifhed from Wheat, Corn, Sfc. which are mowed or reaped. Of this kind are all that grow in Pods, as Beans, Peafe, &c. In the general, all Plants, which have a Papilionaceous, or But- terfly-like Flower, are reckoned by Mr. Ray among the Legttm'tna. The word Legumen t according to Varro and Servius, is formed ex eo quod Mann legatur, £■? nonfecatur j in regard it is gathered -with the Hand, and not cut.
LEMMA, a Term chiefly ufed in Geometry. It figni- fies an AfTumption, or preparatory Proportion, laid down to clear the way for fome following Demonftration : frequently prefix'd to Theorems, in order to render their Demonftration lefs perplcx'd and intricate, and to Pro- blems in order to make their Refolution more eafy and fhort. Thus to prove a Pyramid one third of a Prifm, or Parallelepiped, of the fame Bafe and Height with it ; the Demonflration whereof in the ordinary way, is diffi- cult and troublefome, this Lemma may be premifed, which is proved in the Rules of Progreflion 5 That the Sum of the Series of the Squares in Numbers in Arithmetical Progreflion, beginning from o, and going on 1, 4,0, 16, 25, %6,^c. is always fubtriple of the Sum of as many Terms equal to the greatcft 5 or is always j of the greateft Term multiplied by the Number of Terms. Thus to find the Inflection of a Curve Line, this Lemma is firft premifed 5 ThataTangent may be drawn to the given Curve in a given Point. Thus in Phyfcs, to the Demonflration of molt: Proportions, fuch Lemmata as thefe are neceffary firft to be allowed '■> That there is no Penetration of Di- menfions ; That all Matter is divifible ; and the like. As alfo in the Theory of Medicine, That where the Blood circulates, there is Life, £j?c.
LEMNIAN EARTH, a Medicinal Aftringent, ufed in the fame Cafes as Bole, which fee. It hath its Name from the I {land of Lemnos, whence it is chiefly brought : Many form it into roundCakes, andimprefs a Seal upon it, whence it is call'd Terra SigtUata,
LEMONADE, a Drink prepared of Water, Sugar, and Citrons or Lemons. This factitious Liquor is fo popular in Taris, that it has given its Name to a new eflablifVd Company, call'd Lemonadiers.
LEMURES, Sprites, Hobgoblins ; Refllefs Ghofts of departed Perfons, who return to torment the Living. Thefe are the fame with the Larva, which the Antients imagined to wander round the World, to frighten good People, and plague the bad. For this reafon, at Rome they had their Lemur alia, or Feafls inftituted to appeafe the Mines of the Defunct. Socrates explains the Manes thus: The Soul of Man releafed from the Bands of the Body, and freed from performing his bodily Functions, becomes a kind of Demon or Genius, formerly called Le~ mures. Of thefe Lemures, thofe that were kind to their Families, were called Lares Familiares ; but thofe, who for their Crimes were condemned to wander continually without meeting with any Place of Reft, and terrified good Men, and hurt the bad, were vulgarly called Larva. An anticnt Commentator on Horace mentions, that the Romans ufed the Term Lemures for Remitra j which laft
Word was farmed from Remus, who was kill'd by his Brother Romulus, and who returned to Earth to torment him. But slpiueius obferves, that in the antient Latin Tongue Lemures fignified the Soul of a Man feparated from the Body by Death.
LEMURlA,or LewW^theNameef aFeaftfolemni- zed at Rome on the ninth of May, to pacify the Manes of the Dead, orin honour of the Lemures. The Inftimtion of this Feaft is afcribed to Romulus, who to rid himfelf of the Phan- toms of his Brother Remus (whom he had ordered to be murdered) appearing always before him, ordained a Feaft called after his Name Remuria, and Lemuria. They of- fered Sacrifices for three Nights together, during which time all the Temples of the Gods were fhut up, nor any Marriage permitted. There were a world of Ceremonies in this Feaft, chiefly intended to exorcife the Lemures, and to prevent their appearing or giving any disturbance to the Living.
LENITIVE, in Phytic, is any foftening refolutivc Re- medy, that moiftens the Part difeafed, and diflipates any fharp Humour collected there. Lenitive, in Pharmacy, is a gentle Electuary, compofed of Sena, Polypody, £f?c. fo called in regard it purges eafily, and by refolving.
LENS, in Dioptricks, is any Glafs (not very thick) which either collects the Rays of Light into a Point, in their paflage through it, or difperfes them further apart, according to the Laws of Refraction. Lens's have va- rious Figures ; that is, are terminated by various Surfaces, from which they acquire various Names. Some are plane on one fide, and convex on the other ; others convex on both fides 5 both which are ordinarily called Con- vex Lens's ; tho when we fpeak accurately, the former is call'd I'lano-Convex- Again, fome are plane on one fide and concave on the other, and others are concave on both fides, which are both ufually rank'd among the Concave Lens's 5 tho when diftinguifh'd, the for- mer is call'd a Piano-Concave. Others again are con- cave on both fides ; others are concave on one fide, and convex on the other, which are call'd Convexo- Concave or Concavo-Convex Lenses, according as the one or the other Surface is more curve, or a Portion of a lefs Sphere. It is to be here obferv'd, that in every Lens terminated in any of the forementioned manners, a right Line perpendicular to the two Surfaces is call'd the Axis of the Lens. Which Axis, when both Surfaces are fphe- rical, pafTcs thro both their Centres 5 but if one of em be plain, it falls perpendicularly upon that, and goes thro the Centre of the other.
For Convex Lens's, the Laws of their Refraction, and their Effects depending thereon, are as follow.
A Ray of Light E G near the Axis, (Fig. r. Plate Op- ticks') and parallel thereto, linking on the plane Surface of a Piano-Convex Lens, directly oppofite to the lumi- nous Body, after Refraction concurs with the Axis in the Point F ; and if C be the Centre of the Convexity, CF will be to CL, that is, the Diftance of the Centre from the Point of Concourfe or Focus, will be to the Diftance of the Centre from the Convex Surface, in the Ratio of the Refraction. See RefraHion.
For the plane Surface being directly oppofed to the luminous Body, the Ray E G is perpendicular to A B, and therefore will pafs unrefracted to H : Thus it flrikes on A H B flill parallel to the Axis j and therefore coming out of a denfer Medium into a rarer, will meet the Axis of the Lens in F, and fo, as that C F will be to E L in the Ratio of the Sine of the refracted Angle to the Sine of the Angle of Inclination. As will be demonftrated under the Head RefraBion.
Cor. If then the Refraction be out of a Glafs Lefts into Air C F : E L : : 3 : 2, and therefore F L = 2 CL. That is, parallel Rays near the Axis will concur with it at the diftance of the Diameter. Again, if the Refraction were out of a Water-Lens, i. e. out of a Piano-Convex Lens fill'd with Water, C F : E L = 4 : 3, and therefore E L = 3CL. i.e. parallel Rays near the Axis will concur with it at the diftance of half the Diameter. So that if a lighted Candle be placed in the Focus of a Piano- Convex Lens, that is, in the Point F, diftant from the Surface of the Lens ALB, by the length of the Diameter, and from the Surface of the Water-Lens, by half the Dia- meter, its Rays after Refraction will become parallel. See RefraB'wn.
If the Ray K I (Fig. 2. Plate Optich) near the Axis of a Tlano-Convex Lens, and parallel thereto, ftrike on its convex Surface A H B, after a double Refraction it will meet the Axis in F; fo as that H G will be to GC, and G E to F H in the Ratio of the Refraction.
For the Ray K I, parallel to the Axis E G, by virtue of the firft Refraction in I, will tend to the Point G, fo as G H will be to G C in the Ratio of the Sine of the Angle of Inclination to the Sine of the Refracted Angle: therefore by virtue of the fecond Rcfraclion in L, it will Uuuuu concur
