B E F 



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B E P 



its direction. These bodies have 

 therefore exercised 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 appear to be 

 more elevated than they really are ; 

 because the rays of light moving 

 through the atmosphere in straight 

 lines, are continually inflected to- 

 wards the earth. Light passing 

 obliquely out of a rare into a 

 denser medium, as from vacuum 

 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. 



BEFBA'CTION DOUBLE. When a ray 

 of light passes obliquely from one 

 medium to another of a different 

 density, it is refracted, or bent 

 from its original direction. Still, 

 the image of any object, seen 

 through a refracting medium, usual- 

 ly appears single. There are, how- 

 ever, some transparent minerals, 

 which have the remarkable pro- 

 perty 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 

 object. This is a distinctive cha* 

 racter of very considerable value in 

 some minerals, not depending on 

 any accidental circumstances, but 

 on the nature of the mineral. 

 Double refraction is exhibited most 

 strikingly in Iceland spar. 



BEFEA'CTOEY. A term applied to 

 minerals when they possesss the 

 property of resisting the application 

 of strong heat ; it is also used for 



such as are so tough as to with- 

 stand repeated blows. 



BEFEIGEEA'TION. (refrigeration, Fr.) 

 The act of cooling down ; the state 

 of being cooled 



It is the opinion of some geolo- 

 gists that the whole of this planet 

 was formerly in an incandescent 

 state, and that the process of refri- 

 geration has been constantly pro- 

 ceeding ; that the crust of the 

 earth has cooled down to its present 

 temperature, but that the centre of 

 the earth is still a molten mass. 

 Professor Whewel, speaking of 

 Fourier's arguments on the subject, 

 says, " it results from Fourier's 

 analysis that at a depth of twelve 

 or eighteen miles the earth may be 

 actually incandescent, and yet that 

 the effect of this fervent mass upon 

 the temperature at the surface may 

 be a scarcely perceptible fraction of 

 a degree. The slowness with which 

 any heating or cooling effect would 

 take place through a solid crust is 

 much greater than might be sup- 

 posed. If the earth below twelve 

 leagues depth were replaced by a 

 globe of a temperature five hundred 

 times greater than that of boiling 

 water, 200,000 years would be 

 required to increase the temperature 

 of the surface one degree." 



BE'NIFOBM. (from ren, a kidney, and 

 forma, form, Lat.) Kidney- shaped. 



BE'PTILE. (reptilis, Lat. reptile, Fr. 

 rett'ile, It.) A vertebrated, cold- 

 blooded, animal. The body covered 

 with a shell, or with scales, or 

 entirely naked. Possessing neither 

 hair, mammaB, feathers, nor radi- 

 ated fins; breathing through the 

 mouth and nose by means of lungs ; 

 oviparous, but never hatching its 

 eggs, and amphibious. 



BEPTI'LIA. Beptiles form the third 

 class of vertebrated animals, which 

 is subdivided into four orders, name- 

 ly, Chelonia, or tortoises, Sauria, 

 or lizards, Ophidia, or serpents, 

 and Batrachia, or frogs. Beptilia 



