220 ANSWEHS TO PRACTICAL QUESTIONS 



" Because the light from above, having to pass through 

 a less amount of air, is less obstructed than that which 

 comes horizontally. It is therefore more vivid." 



53. Why do the two parallel tracks of a railroad appear 

 to approach in the distance ? 



This depends upon what is known in painting as the 

 vanishing point. " Suppose two long rows of pillars, 100 

 feet apart, and an observer standing at one end looking 

 down the rows. Evidently, for the same reason as the 

 space between the top and bottom of the pillars, that is 

 to say their height, becomes apparently less and less as 

 their distance from the eye increases, so will the space 

 between each pillar and its opposite in the ether row 

 become apparently less, and the lines of pillars will, at a 

 certain distance (viz., where 200 feet are apparently 

 reduced to a poinO, seem to join. Beyond that spot, 

 known as the vanishing point, none of the pillars can be 

 seen." 



(Read Arnott's Physics, pp. 616-622.) 



54. Why does a fog magnify objects ? 



The fog diminishes the intensity of the light. The 

 visual angle, however, remains the same. " An object at 

 two miles, subtending the same angle as an object at one 

 mile, is twice as broad, and the conclusion is drawn that 

 the dim object is large. Thus, a person in a fog may 

 believe that he is approaching a great tree fifty yards 

 distant, when the next instant throws him into a low 

 bush that has deceived him. A boy on the stage, with 

 a thin gauze screen before him, will look to the audience 

 like a man in the distance." 



(See Arnott's Physics, p. 6a8.) 



