Man's physical universe



inverted; (3) if tiie object is placed still farther away, the image will


Fig. 205. An all-glass driving

lamp, similar in construction to a

sealed-beam headlight except that it

employs one filament instead of two

filaments. (Courtesy of the General

Electric Company.)

be inverted, but it will be larger than the object.

The bowl of a spoon or the sidcrcar-vicw

mirror of an automobile

are convex mirrors, in which the

image is always smaller than the


Sealed-beam reflectors were introduced

on automobiles in 1940.

These headlights seal the interior

from dust and moisture and thus

preserve the reflecting surface. One

type of sealed-beam headlight uses

a silver-plated brass reflector, a

lamp, a glass lens, and a gasket,

while a second type uses a glass

lens fused to a glass reflector filled

with argon gas in which the lamp

filaments are located without the

use of a separate bulb.

The use of offset filaments in an

automobile headlight controls the

beam in the two-beam headlight

system. See Fig. 206. By placing

one filament slightly to the side of

the other, the beam that tilts down also turns somewhat to the right.

See Fig. 207.

The Refraction of Light Explains Many Phenomena.

The velocity of light is different in media of different densities. A

crucial test of the two theories of light was based on this fact. Accord-



Fig. 206.

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