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RECE'PTACLE. (receptaculum, Lat. recep- 

 tacle, Fr. ricettacolo, It.) In botany, the 

 basis or point, upon which all the parts 

 of the fructification rest ; the receptacle 

 has not always any particular figure to 

 distinguish it, except in compound flowers, 

 when the surface, which is either convex, 

 concave, conical, scaly, cellular, hairy, or 

 naked, forms the distinguishing character 

 of the genus or family. The receptacle 

 is distinguished into receptaculum pro- 

 prium, or receptacle appertaining to one 

 fructification only ; and receptaculum 

 commune, or common receptacle, con- 

 necting several distinct fructifications. 



RECLI'NED. In botany, applied to leaves 

 when the point is lower than the base ; 

 also to stems when curved towards the 

 ground. 



RECTA'NGLE. (rectangulus, Lat. rectangle, 

 Fr.) Every right-angled parallelogram 

 is called a rectangle, and is said to be 

 contained by any two of the straight 

 lines which contain one of the right 

 angles. 



RECTA'NGLED. Having a right angle, or an 

 angle of ninety degrees. 



RECTA'NGULAR. (rectangulaire,r.') Right 

 angled ; having one or more angles of 

 ninety degrees. 



RECTILI'NEAL. ^ (from rectilineus, Lat. 



RECTILINEAR. )> made of straight lines, 



RECTILI'NEOUS.J rectiligne, Fr.) Con- 

 sisting of right lines ; right lined ; in a 

 straight line. 



RECU'RVATED. ^ (from re, back, and curvo, 



RECI/RVED. $ to bend, Lat.) Bent 

 backwards ; turned backwards. 



RED CO'RAL. (the corallium rubrum.} A 

 branched zoophyte, somewhat resembling 

 in miniature a tree deprived of its leaves 

 and twigs. It seldom exceeds one foot 

 in height, and is attached to the rocks by 

 a broad expansion or base. It consists of 

 a bright red, stony axis, invested with a 

 fleshy, or gelatinous substance of a pale 

 blue colour, which is studded over with 

 stellular polypi. Dr. Mantell, Wonders 

 of Geology. 



RED CHALK. See Reddle. 



RED MARL. Another name for the new red 

 sandstone. 



RE'DDLE. The roethel of Werner ; the 

 crayon rouge of Brochant ; the argile 

 ocreuse rouge graphique of Haiiy. Red 

 chalk ; a species of argillaceous iron-stone 

 ore. The best specimens are brought 

 from Germany. It occurs in opaque 

 masses, having a compact texture. In 

 hardness, it differs but little from chalk. 

 It is dry, and rough to the touch, ad- 

 hering to the tongue, and yielding an 

 argillaceous odour. Specific gravity from 

 3-10 to 3-90. 



REEF, (riff, Germ.) A range of rocks 



lying generally near the surface of the 

 water. 



REFLE'CT. (reflecto, Lat. rejlfo/tir, Fr. 

 riflettere, It.) To throw back ; to return. 



REFLECTED, (refiechi, Fr.) Folded back- 

 wards ; thrown back. 



REFLECTION. The act of throwing back ; 

 the act of bending back ; that which is 

 reflected. By the laws of optics, the 

 angle of reflection is equal to that of inci- 

 dence, whatever the reflecting surface 

 may be, and however obliquely the light 

 may fall upon it. 



REFLE'XED. Recurvated ; bent backwards. 



REFRA'CTED. 



1. In conchology, abruptly bent, as if 

 broken. 



2. In botany, bent back at an acute angle. 

 REFRA'CTION. (refraction, Fr. refrazione, 



It.) The incurvation, or change of deter- 

 mination in the body moved, which hap- 

 pens to it whilst it enters or penetrates 

 any medium ; in dioptricks, it is the 

 variation of a ray of light from that right 

 line, which it would have passed on in, 

 had not the density of the medium turned 

 it aside. When light passes through a 

 drop of water or a piece of glass, it ob- 

 viously suffers some change in its direc- 

 tion. These bodies have therefore exer- 

 cised some action, or produced some 

 change upon the light, during its progress 

 through them. The power which thus 

 bends or changes the direction of a ray of 

 light is called refraction, and the amount 

 of this refraction varies with the nature 

 of the body. All the celestial bodies ap- 

 pear to be more elevated than they really 

 are ; because the rays of light moving 

 through the atmosphere in straight lines, 

 are continually inflected towards the 

 earth. Light passing obliquely out of a 

 rare into a denser medium, as from va- 

 cuum into air, or from air into water, is 

 bent or refracted from its course towards 

 a perpendicular to that point of the 

 denser surface where the light enters it. 

 The denser the medium the more the 

 ray is bent. Mrs. Somerville. Brewster. 

 Herschel. 



REFRA'CTION DOUBLE. When a ray of 

 light passes obliquely from one medium 

 to another of a different density, it is re- 

 fracted, or bent from its original direc- 

 tion. Still, the image of any object, seen 

 through a refracting medium, usually ap- 

 pears single. There are, however, some 

 transparent minerals, which have the 

 remarkable property of causing objects to 

 appear double ; that is, they present two 

 images of any object seen through them. 

 In this case it is evident, that the ray 

 must be divided into two portions after 

 entering the refracting medium, and that 

 each portion presents an image of the 



