Man's physical universe

xanabras

POLARIZED LIGHT 431

seeing equally well through both lenses and, therefore, with both eyes.

$50,000 claim for damages was thrown out of court.

Crack railroad trains speeding over western plains are light-conditioned as

well as air-conditioned. Light conditioning is made possible by windows of

two polarizing discs with flat surfaces against each other. They are mounted

in such a way that the outer disc is set stationary to block all reflected glare

while the inner disc can be moved by turning a knob, whenever the passenger

wants to reduce or increase the amount of light that enters the car. Exactly

the same principle is used in new variable sun glasses which enable the wearer

to reduce the brilliance of a scene simply by touching a button on the glasses.^

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STUDY QUESTIONS

1. What is polarized light?

2. In what three diff'erent ways may light be polarized?

3. What is a Nicol prism, and for what is it used?

4. What is the nature of a Polaroid screen?

5. Explain how the glare from streets, snow, sand, or water is removed by

Polaroid screens.

6. Explain how the glare from automobile headlights could be removed by the

use of Polaroid screens.

7. Why are the axes of the visor and the headlights in the polarized-light system

proposed for automobiles arranged parallel and 45° to the road?

8. Explain why the blueness of the sky depends upon the clarity of the air.

9. How can one prove that the light scattered by the molecules of the atmosphere

is polarized?

10. Explain how the intensity of light may be controlled by the use of Polaroid

screens.

11. Why do Polaroid day glasses intercept the glare from only horizontal surfaces?

12. What are the advantages in the use of Pola screens in photography?

13. Explain the use of polarized light in detecting strains in transparent materials.

14. Explain how three-dimensional pictures are made possible by Polaroid

screens.

15. Show how polarized light was used to trap a woman who falsely claimed

damaged eyesight.

1 From Science News Letter, November 9, 1940, p. 294.

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