294 DETAILED SYNTHESIS. 



most beautiful Black is a sensation produced when no light is acting 

 on the organ of sight. It is not, however, a negative, but a positive 

 sensation. 



755. SOME OBJECTS give off, others transmit, and 

 others reflect, one or two, or all kinds of light, while 

 some do neither. 



756. Illus. THE SUN is the only source of all kinds of light hi 

 perfect proportions. Many objects, candles, etc., give off all kinds, but 

 not in perfect proportions. Some give off but one or two varieties. 

 Glass transmits all kinds well, but the front parts of the eye most per- 

 fectly. Some objects transmit one or two, and not more. Looking- 

 glass, a sheet of water, polished surfaces, etc., reflect all kinds. All 

 objects, except "good reflectors," and black, reflect some kinds, but not 

 others. Grass reflects blue and yellow ; blood reflects red chiefly. 



757. Those objects that give off, transmit, or reflect 

 any kind or kinds of light, are correspondingly CALLED 

 WHITE, BED, GREEN, ETC., OBJECTS. That an object may 

 appear black, it is only necessary that it should neither 

 give off, transmit, nor reflect any light. (See Figs. 10 to 

 17, PI. 8.) 



758. OBJECTS THAT PRODUCE OR REFLECT LIGHT, EX- 

 CEPT GOOD REFLECTORS, throw it off in all directions in 

 straight lines. 



759. GOOD REFLECTORS AND THOSE OBJECTS THAT 



TRANSMIT LIGHT, throw the light only in certain direc- 

 tions, depending upon their form, their density, and the 

 direction in which light has fallen upon them. 



760. Illus. A SUN-GLASS (convex lens), properly exposed to the 

 sunlight, will bend (refract) the light as it enters, and again, as it leaves, 

 in such a manner that all which enters will be brought, just beyond the 

 lens, to a single, very bright point, called a focus. 



761. As LIGHT COMING FROM TWO DIFFERENT POINTS 



to the lens must come from different directions, the lens 

 must bend them to different foci; and every point which 

 can throw light upon the lens will be represented by a 

 focus on the other side of the lens. 



755. What said of ? 756. What said of ? 757. What are ? 758. What 

 said of ? 759. What said of ? 700. What said of ? 761. What said of ? 



