National Geographic : 1920 Jul
THE NATIONAL GEOGRAPHIC MAGAZINE O Underwood and Underwood OPERATING TIHE POLARISCOPE IN A SUGAR-MILL LABORATORY If a wind is blowing through a paling fence, only the straws carried in a vertical position by 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 boy is so eager to answer that as a class they seem almost to fall over themselves in their effort to be 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 0. Henry will be widely taught in the public schools.