50 ANSWERS TO PRACTICAL QUESTIONS 



it is thought that the azure of the sky would not be seen, and 

 the heavens would appear black : the illumination of objects 

 would be strong and glaring on one side, and on the opposite 

 side the shadows would be deep and unrelieved by the diffused 

 light to which we are accustomed. The minute particles of va- 

 por in the air serve to scatter the direct rays of the sun, and to 

 turn them around corners and into places not in the direct line 

 of the sunlight. 



(See a full and interesting discussion in Tyndall's Lecture on Light, p. 

 152, et seq,) 



57. IVliy does skim -milk look blue and neiv milk 

 white ? 



The fatty globules of the new milk reflect all the colors of 

 the spectrum to the eye ; but when deprived of the cream the 

 milk reflects the blue light in excess of the others. 



58. Why is not the image of the sun in water at mia^ 

 day so bright as near sunset ? 



The angle of incidence being small, most of the light is 

 transmitted, and but little is reflected. Near sunset the greater 

 part is reflected. 



59. Why is the rainboiv always opposite the sun ? 



(See Physics, p. 217.) 



60. Sold a card with its edge close in front of your eye 

 and look at a distant candle flame in a dark room. You 

 will probably perceive either a reddish or a bluish fringe 

 on one side. Explain. 



The crystalline lens is not corrected for chromatic aberra- 

 tion. (See Physics, p. 219.) 



HEAT. 



273 1. Wtiy will one's hand, on a frosty morning, 

 freeze to a metallic door-knob sooner than to one of porce- 

 lain ? 



Because the metal is a better conductor of heat than the 

 porcelain, and hence conducts the heat from the hand faster. 



