Man's physical universe

xanabras

70 THE UNIVERSE A VAST SYSTEM OF PARTS

a "collimating lens." The other tube also contains a lens to carry the

image of the spectrum to the eye. As one views the light which is a

mixture of all visible light rays through a spectroscope, the resulting

spectrum appears as a series of beautiful colors like a cross section of a

rainbow.

A continuous spectrum (that produced by light from an incandescent

solid or liquid surface) is found to vary in intensity at different positions.

This variation in the intensity of different wave lengths is connected

with the temperature so that the spectrometer enables one to

determine the temperature of an incandescent body by analyzing the

light which it emits.

The spectrum obtained from a luminous gas is called a bright-line

spectrum because it is not continuous but contains certain narrow

lines or bands of color. Inasmuch as light has its origin within the

smallest molecular and atomic electrical systems of matter, it is not

surprising to learn that the analysis of light from any given source

reveals an enormous amount of information concerning that source.

There is a definite position for each of the bright lines, which is always

the same for the same element of matter.

Not only do the elements,^

such as hydrogen, nitrogen, and helium, show characteristic spectra,

but so likewise do many compounds of these elements. By the use of

the spectroscope man is thus able to analyze samples of matter on the

earth and determine their composition.

Joseph Fraunhofer (1787-1826) observed a number of distinct dark

lines of varying width vertically across the continuous spectrum which

He carefully noted the position of about

he obtained with sunlight.

600 of these lines, which have been named Fraunhofer lines in his

honor; but he failed to explain their significance.

Kirchhoff's discovery of bright-line spectra in 1859, coupled with the

later momentous discovery that light rays from a luminous gas, when

passed through a cool, nonluminous layer of the same gas, would

produce dark bands at the exact position of the bright lines produced

by the gas under ordinary conditions, provided the key to a vast storehouse

of knowledge concerning the universe. At last the Fraunhofer

lines were explained. They must have been produced by the passing

of the sun's rays through the envelope of cooler gas surrounding the

sun, which itself is thought to be a huge mass of luminous gas. The

bright-line spectra of known elements on the earth were found to coincide

with the position of many of the Fraunhofer lines, so that it was

soon learned that such elements as sodium, carbon, iron, copper,

'

An element is one of the 92 different kinds of matter that cannot be decomposed into

simpler kinds of matter by ordinary chemical means.

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