Man's physical universe



an iodine solution. This new screen transmits one-third more light

than the previous Polaroid screen and polarizes 99.99 per cent of the

light to which the eye is most sensitive.

Light May Also Be Polarized by Reflection.

When light strikes a glass plate at an angle, about 5 per cent of the

light is reflected, and a portion of this reflected light will be polarized.

A pile of glass plates not only produces polarized light by reflection

Fig. 188. You can see perfectly

through several thicknesses of Polaroid

if their "optical slots" are parallel,

as they are in the roll at the left.

But when the "slots" of the material

are crossed, as they are in the fold at

the right, no light passes and you

cannot see through. (Courtesy of

The Polaroid Corporation.)

but polarizes the transmitted light

much as crystals do. The angle of

a glass plate or mirror relative to

the direction of the beam of light

determines the relative amounts of

ordinary reflected

light and plane

polarized light. The best angle,

called the angle of polarization, is

about 57 degrees for ordinary glass.

Direct glaring reflections of sun

and sky from the sea and asphalt

or concrete pavements are polarized

to a fairly high degree, while

the diffuse reflections used in vision

are not. By using a polarizing sun

glass, it is possible to block the

glare while transmitting the useful


Light May Be Extinguished by Use


of Crossed Polarizers.

187 shows how a second

Polaroid disk placed perpendicular

to the axis of the first Polaroid

disk will not permit the light which is polarized by the first disk to

pass through the second disk.

Figure 189 shows how the use of polarizing screens on headlights

and windshields would eliminate automobile-headlight glare.

Inasmuch as nearly 60 per cent of light is absorbed when it passes

through a polarizing screen, headlights would have to be two or three

times as powerful as present headlights when using polarizing screens.

The benefits of polarizing screens would be proportional to the number

of cars equipped with them.

Each car is fitted with a windshield visor of Polaroid, with its "slots"

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