28 'LIGHT. 



12. Light is not simple. It is composed of seven colors, as 

 separated by the triangular glass prism, in the following order. 



300 



Red, Orange, Yellow, Green, Blue, Indigo, Violet.* 

 45 27 48 60 40 80 



beginning with the least, and ending with the most refrangible. 



" Dr. Wollaston found that when a beam of light only one twen- 

 tieth of an inch broad is received by the eye, at the distance often feet, 

 through a clear prism of flint glass, only four colors are seen, viz : 

 red, yellowish green, blue, and violet. The different rays being again 

 collected by a lens into a focus, produced uncolored light." H. 



13. LIGHT is CONTAINED IN ALL BODIES. 



It appears to be both inherent in them, and to enter them from 

 without. 



(a.) It passes through some without any sensible obstruction 

 they are therefore transparent, as glass, air, rock crystal, &ic. 



Other bodies partially arrest the light, and others still allow a little 

 to pass, while some stop it entirely ; this gives origin to the terms, 

 transparent, semi-transparent, translucent, and opake. " 



Strictly, no visible body is transparent, and therefore aerial bodies 

 are really the only ones that are perfectly transparent, f and even they, 

 become in a degree visible, in consequence of the disturbed refraction 

 of light. 



(b.) Diversity of color is produced by the absorption of some 

 rays and the reflection of others. 



White bodies reflect all, and black absorb all, or nearly all, with- 

 out decomposition; when a body appears red, green, yellow, blue, 

 &c. all other rays are absorbed and these are reflected. All per- 

 sons do not perceive colors- we may very possibly find one such 

 person, or more, in every considerable assembly, and many such in- 

 stances might be collected. Harris, a shoemaker at Allonby in Eng- 

 land, could distinguish only black and white ; when a child, he could 

 not distinguish the cherries on a tree from the leaves, except by their 

 form and size. Mr. Scott could not distinguish green. Pink and 

 pale blue appeared alike, and so did red and full green which he 

 thought a good match ; several of the relations had similar defects. J 

 A tailor repaired a black silk and a blue coat with crimson. f 



* Quoted from Henry, 10th Edit. Vol. I. p. 156. Blue is not mentioned in as- 

 signing the relative spaces, although it is mentioned in the list of colors; other au- 

 thors assign 60 to blue, dividing the whole spectrum into 360. 



t Except chlorine, and one or two others. 



t Ph. Tr. 1777, and 78, and 80. L. u. K. A gentleman of my acquaintance 

 bought and wore a scarlet dress supposing it to be drab ; still he was a good judge 

 of pictures. I have known several such examples. 



