R E F 



R E F 



vvhicli is the fame thing as the fun's cleclinaWon iu the 

 Ptoli?niaie fyftem. 



RErLECTiON is alfo ufed figuratively for an operation of 

 the mind, by which, turning as it were back upon itfdf, 

 it makes itfclf, and its own operation, its objeft ; and con- 

 fiders or contemphitus the manner, order, and laws, whicli 

 it obferves ni perceiving, rcafoning, willing, judging, doubt- 

 ing, believing, &c. and frames itfelf new ideas of the re- 

 lations difcovered in them. 



REFLECTOIRE Curve. See Cu-rve Rejleaoire. 



REFLECTOR for Light-houfes, a combination of a 

 number of Iquare plane glafs mirrors, refembling thofe with 

 vvhicli Archimedes is faid to have burnt the Roman fleet at 

 the fiege ef Syracufe. (See BuRNiNC-G/a/r.) Each of 

 thefe mirrors is about an inch fquare ; and they are all ar- 

 ranged clofe to each other in the concave of a parabolic feg- 

 ment formed of Itucco, which has been found to anfwer the 

 purpofe beft. The idea of thus illuminating light-houfes, 

 inftead of ufing coal-fires, in this country, without any pre- 

 vious knowledge of a fimilar method praftifed in France, 

 was iirft fuggeited by Mr. Ezekiel Walker, of Lynn Regis, 

 who made, and fixed up refleftors under his diredlion, in a 

 light -houfe on the coaft of Norfolk, in the year 1779. Ac- 

 cordingly, in the year 1787, at the requeil of the truftees 

 appointed by aft of parliament for erefting four light- 

 houfes in the northern parts of Great Britain, he inilrufted 

 Mr. Thomas Smitli, tin-plate worker, of Edinburgh, to 

 whom the original invention is erroneoufly afcribed in the 

 fupplement to the Encyclopedia Britannica, in this mode of 

 conllrufting light-houfes. His parabolic moulds are from 

 three to five or fix feet in diameter ; and in the centre or apex 

 of each is placed a long fhallow lamp of tin-plate, filled 

 with whale-oil. In each lamp are fix cotton-wicks, almoll 

 contiguous to one another, fo difpofed as to burn without 

 trimming for fix hours. The light of thefe is reflefted from 

 each mirror fpread over the concave furface, and is thus mul- 

 tiplied, as it were, by the number of mirrors. The ttucco 

 moulding is covered on the back with tin-plate, from which 

 a tube, immediately over the lamp, proceeds to the raof of 

 the light-room, and ferves as a funnel, through which the 

 fmoke efcapes without fuUying the faces of the mirrors. 

 The light room is a cupola or lantern of from eight to twelve 

 fides, compofed entirely of glafs, fixed in call iron frames 

 or falhes, and roofed with copper. On circular branches 

 pafling round the infide of this lantern, at about 18 inches 

 from the glafs frames, are placed the refleftors with their 

 lamps, fo as that the concave lurfaces of two or three of the 

 refleftors front every point of the compafs, and throw a 

 blaze of light in all direftions. In the roof, immediately 

 over the centre of the room, is a hole, through which pafs 

 all the funnels already mentioned, and which ferves likewife 

 to admit frefii air to the lamps. This hght-room is firmly 

 fixed on the top of a round tower, fo as to be immoveable 

 by tlie weather ; and the number of the refleftors, and tlie 

 height of the tower, are lefs or greater according as it is in- 

 tended that the light thould be feen at a lefs or a greater dif- 

 tance. Experience, it is faid, has obviated feveral objeftions 

 to which light-houfes of this kind were thought to be 

 liable ; and it has been found that light-houfes, with 

 lamps and refleftors, are, in every point of view, pre- 

 ferable to thofe with fires burning in the air. They 

 are fupported at a much Icls expeuce ; their hght is more 

 brilliant, and feen at a greater diltance, whilft it can 

 never be obfcured by fmoke, or beaten down, on the lee- 

 fide, by a violent gull of wind ; and they may be fo va- 

 rioufly placed, that one hght-houfe cannot be miftaken for 

 another. Befides, the lamps do not need trimming fo often 



Vol. XXIX. 



as open fires require fuel, and the man who attends them ia 

 never cxpofed either to cold or wet in the performance of his 

 duly, fo that they are lef;; likely to be neglcfted in Itormy 

 weather than thofe with open fires. 



It has been propofed to make the concave furface of the 

 parabola one fpcculum of metal, inllead of covering it over 

 with a number of plain glafs mirrors ; or to diminifli the fize 

 of each mirror, if it be thought beil to retain them inftead 

 of introducing the fpeculnm. To this propofed alteration 

 it has been objefted, that the brightell metal does not refleft 

 fuch a quantity of light as well foliated clear glafs ; and by 

 diminifliing the fize of the mirrors, the number of joinings 

 would beincreafcd, in each of which fome light is loft, not 

 merely in the feam, but from its being ahnolt inipoffible to 

 foliate glafs perfeftly at its edge. 



REFLEX, Reflect, in Painting, is underftood of thofe 

 places in a piiSure which are fuppofed to be illuminated by 

 a light reflefted from fome other body reprefented in the 

 fame piece. 



Or, reflexes may be defined thofe places which, befide 

 the general light that illumines the whole piece, receive fome 

 particular light from their fituation with refpeft to fome 

 more illummated polifhed body, that reflefts part of the 

 rays it receives upon them. 



Reflexes are fcarcely fenfible, except in the fliadowcd 

 parts. The management of the reflexes requires great ac- 

 curacy and fliill. All reflefted light is fuppofed to carry 

 with it part of the colour of the body which reflefts it ; fo 

 that thofe places which receive this light, muft have their 

 colour mixed or tinged with that colour. But the fame 

 place may receive reflexes from different objefts, differently 

 coloured, and thofe again receive reflexes from others. The 

 painter, therefore, muft have a view to every circumftance 

 of the colour, light, and pofition of each figure ; he muft 

 confider what eff'eft each has on others, and purfue nature 

 through all the variety of mixtures. See Clair-obscure, 

 and Light. 



Reflex Fi/ion, or Reflected vijion, is that performed 

 by means of rays reflefted from the pohflied furfaces of ob- 

 jefts to the eye. 



Reflex vifion is the fubjeft of catoptrics. Under reflex 

 vifion come all the phenomena of fpecula or mirrors of all 

 kinds. 



REFLEXIBILITY of the Rays of Light, is that pro- 

 perty by which they are difpofed to be reflefted. See Re- 

 flection. 



Or, it is their difpofition to be turned back into the fame 

 medium, from any other medium on whofe furface they fall ; 

 hence thofe rays are laid to be more or lefs reflexible, which 

 are returned back more or lefs eafily under the fame inci- 

 dence. 



Thus, if light pafs out of glafs into air, and by being in- 

 chned more and more to the common furface of the glafs 

 and air, begins at length to be totally reflefted by that fur- 

 face, thofe forts of rays which at like incidences are reflefted 

 moft copioufly, or the rays which, by being inchned, 

 begin fooneft to be totally reflefted, are the moft reflexible 

 rays. 



That rays of light are of different colours, and endued 

 with different degrees of reflcxibility, was firft difcovered 

 by fir Ifaac Newton ; and is fhewn by the following experi- 

 ment. Applying a prifm DFE [Plate XVII. Optics, 

 fg. 15.), whofe angles are each 45°, to the aperture C of a 

 darkened room, in fuch manner as that the light is reflefted 

 from the bafe in G ; the violet rays are feen firft reflefted 

 into H G ; the other rays continuing ftill refrafted in I K. 

 After the violet the blue are all refrafted, the green, &c. 

 4 D (See 



