Figure 2-51. Dispersion.

TM 9-258

c. Glass of various optical densities disperses light

heated to a point of incandescence emits light of a

frequency unique to that element, the spectrum of an

to different degress. A prism of flint glass disperses the

incandescent solid can be used to show of what that

rays of different color more than the less optically dense

solid is composed. By the use of the spectroscope,

crown glass. A lens would also separate light because a

helium was discovered in the atmosphere of the sun

lens may be considered as an infinite number of prisms.

before it was discovered on earth.

The properties of different kinds of glass are employed to

e. An instrument similar to the spectroscope but

neutralize the dispersion of the rays of colored light in

fitted with a camera permits the photographing of

lenses and prisms, and to neutralize their tendencies to

spectra.

The photographic records made by this

form different focal points when refracted through lenses

instrument are called spectrographs. This instrument is

d. The principle of dispersion is put to practical use

also used to measure refractive indices and is extremely

accurate.

in a scientific instrument known as the spectroscope.

f. The rainbow is a natural phenomenon resulting

This instrument is especially designed to disperse light

from refraction and total internal reflection of sunlight in

coming from an incandescent source.

Since any

raindrops (B, fig 2-51).

element upon being

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