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THE NATIONAL GEOGRAPHIC MAGAZINE 



© Underwood and Underwood 



OPERATING THE POLARISCOPE IN A SUGAR-MILL LABORATORY 



If a wind is blowing through a paling fence, only the straws carried in a vertical position 

 Ly it can get through. The others are stopped by the fence. In the same way, only those 

 rays of light which are, let us say, upright can get through the prism of a polariscope. 

 These are called polarized rays. If they are passed through a solution of sugar, after passing 

 through the prism, they are no longer upright, but lean to one side, so to speak, and are 

 therefore unable to get through a second prism, which looks dark to the operator. He turns 

 this prism around until its axis is parallel to the plane of the rays of light seeking to pass 

 through it, and the distance he has to turn the prism before the light can come through tells 

 him exactly how much the rays were deflected from an upright position in passing through the 

 sugar, and therefore exactly how pure or impure the sugar solution is (see page 30). 



noun, first person, singular, and 'cry' is 

 the present tense of the verb 'to cry,' " 

 they answer. 



And so it goes. Every bov is so eager 

 to answer that as a class they seem almost 

 to fall over themselves in their effort to 

 lie first. They show a quickness in grasp- 



ing the significance of number, tense, and 

 mood that amazes the beholder. Under 

 such a teacher, learning English is plainly 

 a joy to the pupils. As soon as the teacher 

 problem can be met adequately, the lan- 

 guage of Shakespeare and O. Henry will 

 be widely taught in the public schools. 



