Michelson A. A. Light waves and their uses (1903)

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Light Waves and Their Uses

extends almost to 200 millimeters. The corresponding line is shown to be a close double.

The curve corresponding to the violet light of cadmium is shown in Fig. 68, and is seen to be comparatively simple.

We have thus shown that spectral lines are complex distributions of light, whose resolution in general is beyond the power of the spectroscope. This complexity of the spectral lines is particularly interesting because it indicates a corresponding complexity of the molecules which cause the vibrations which give rise to the corresponding spectral lines.

This complexity may be likened to the complexity of a solar system; and while this may bring dismay to the Keplers and Newtons who may hope to unravel the mysteries of this pigmy world, it certainly increases the interest in the problem.

FIG. 67


Interference Methods in Spectroscopy 83


1. The spectrum of the light emitted by incandescent gases is not continuous, but is made up of a number of bright lines whose position in the spectrum is very definite, and which are characteristic of the elements which produce them.

2. These “lines” are not such in a mathematical sense, but have an appreciable width and a varying distribution of light, and in some cases are highly complex.

3. This variation in distribution is, however, restricted to such narrow limits that in most cases it is impossible to investigate it by the best spectroscopes; but by the method of visibility curves the lines may be resolved into their elements.

4. An important auxiliary for the interpretation of the visibility curves is the harmonic analyzer—an instrument which sums up any number of simple harmonic motions, and which also analyzes any complex motion into its simple harmonic elements.