454 REFRACTION OF LIGHT. 



Objects which are not much smaller than the convex mirror used, 

 and still more objects which are larger than it is, should not be 

 brought too near to the reflecting surface, or the images are much 

 distorted. The images of the more distant objects are smaller than 

 those of the nearer. If a body has comparatively large dimensions, 

 some portions of it will be sensibly nearer to the mirror than 

 others, and will hence appear larger than the images of those portions 

 of the same body which are farther from the mirror : this is the 

 cause of the distortion. If the face be brought near to a convex 

 mirror which is rather small, the projecting parbs of the face for 

 example, the nose will in the image appear larger in proportion 

 than other parts of the face, and the whole will therefore resemble 

 the distorted figure of a human face in a caricature. 



40. Refraction of Light. Prisms. Lenses. When 

 light falls upon the surface of a body, a certain 

 quantity, which varies according to the nature of the 

 surface, is reflected; the quantity of reflected light 

 is the greater, the lighter and more polished the 

 surface, and the less, the darker and rougher it is. Bat 

 even the brightest and best polished metallic mirrors 

 da not reflect the whole of the light which falls on 

 them; a portion of the incident light penetrates in 

 all cases into the interior of the body. If the body is 

 opaque, the light is completely absorbed very near the 

 surface, so that it penetrates only to a very small depth ; 

 if the body is semi-transparent, the light is absorbed only 

 gradually, it penetrates deeper, and may even partly 

 pass through the substance; finally, if the body 

 is transparent, the light is only slightly diminished, 

 but it undergoes mostly a considerable change of its 

 original direction; only those rays of light which 

 are incident in directions perpendicular to the surface 

 of a transparent body are permitted to proceed in their 

 original directions. 



A rectangular water-tight vessel, such as a tin 



