REF 



REF 



period or repetend. A pure circulator is 

 one in which the period begins imme- 

 diately after the point; all others are 

 called mixed. 



RED CHALK. Red clay, or reddle ; 

 an argillaceous iron-stone ore. 



RED FIRE. A pyrotechnical com- 

 pound of nitrate of strontia, sulphur, 

 antimony, and chlorate of potash, which 

 burns with a red flame. 



RED LEAD. Minium. An oxide of 

 lead with a fine red colour, with a shade 

 of yellow. It is intermediate between 

 the protoxide and the peroxide. 



RED MARL. Variegated Red Sand- 

 stone ; a sandstone with an argillaceous 

 cement, often containing beds of red or 

 variegated marl, and subordinate beds of 

 reddish oolite and dolomite, with clays 

 containing gypsum and salt. 



RED PRECIPITATE. The red oxide 

 of mercury, or mercuric oxide, obtained 

 by the decomposition of the nitrate of 

 mercury by heat. 



REDU'CTION. A rule in arithmetic 

 by which we find the quantity in one de- 

 nomination corresponding to a quantity 

 expressed in another denomination; by 

 which, for example, we find how many 

 shillings there are in a certain number of 

 pounds, how many pounds in a certain 

 number of shillings, &c. In the former 

 case the reduction is termed descending, 

 and is performed by multiplication ; in 

 the latter it is ascending, and is per- 

 formed by division. 



REDU'CTION OF METALS. The 

 conversion of the oxides of metals into 

 the metallic state, by the application of 

 heat; the operation consists in mixing 

 them with some substance which will 

 attract the oxygen from the oxides ; coal 

 is the substance generally employed for 

 this purpose. 



REEF, or CORAL REEF. A pecu- 

 liar kind of rock produced by the coral 

 animalcule, found in the ocean, of con- 

 siderable length, of very narrow width, 

 and generally only a few feet below the 

 surface of the water. Reefs are usually 

 of a circular or oval form, surrounded by 

 a deep sea, the interior generally pre- 

 senting the appearance of a shallow 

 lagoon. But they appear under various 

 forms. 



REFERENCES, FALLACY OF. An 

 artifice sometimes employed by dishonest 

 writers, consisting in the merely giving 

 of references to authorities, which may 

 be conceived favourable to the writers' 

 views ; it is supposed that few will take 

 285 



the trouble of examining the passages 

 referred to, and that the confirmation of 

 the writers' statements by such authori- 

 ties will be taken for granted. 



REFINING. The operation of puri- 

 fying anything; particularly the assay- 

 ing or purifying of gold and silver, by 

 separating them from other bodies which 

 are combined with them. 



REFLECTING CIRCLE. An astro- 

 nomical instrument destined for the 

 same uses as the sextant, but more com- 

 plete, the circle being entire, and the 

 divisions carried all round. It is usually 

 furnished with three verniers, so as to 

 admit of three distinct readings off, by 

 the average of which the error of gra- 

 duation and of reading is reduced. 



REFLECTION {reflecto, to bend back). 

 In Physics, this term denotes the re- 

 bound of the rays of light, of heat, or of 

 sound, from an opposing surface. Po- 

 lished surfaces reflect light to the eye, 

 and are, therefore, more generally termed 

 reflectors or mirrors. Heat and sound 

 are reflected without relation to the eye, 

 and are returned from more rugged sur- 

 faces. 



Reflecting microscopes and telescopes 

 are such as carry a magnified image of 

 the object to the eye, by means of rays 

 reflected from a concave speculum. 



REFRA'CTION {refractus, broken 

 back). That property of light, by which 

 a ray becomes refracted, or bent back, 

 when passing in an oblique direction 

 from a rarer into a denser medium, and 

 vice versd. The phenomenon may be 

 observed on immersing one end of a rod, 

 in a slanting direction, in a vessel of 

 water : the part immersed appears as if 

 it were bent, or broken, at the surface 

 of the liquid. This is termed ordinary 

 refraction. 



1. Refraction, double. A property of 

 certain transparent minerals, as Iceland 

 spar, by which a ray of light, after enter- 

 ing such a medium, becomes divided 

 into two portions or rays, each of which 

 presents an imaiie of the object. One of 

 these rays follows the ordinary law of the 

 sines, and the otlier is refracted accord- 

 ing to a new or extraordinary law; hence 

 these two rays have been termed the 

 ordinary ray, and the extraordinary ray, 

 respectively. 



2. Refraction, index of. A term ap- 

 plied to the ratio which subsists between 

 the sines of the angles of incidence and 

 of refraction, which is also in every case 

 a constant ratio. 



