It was a **wavelength** thing—we just meshed.

If D is the measured deviation of a ray, and Do, Xo, c and a are four constants, the equation A=Ao-{ (D - D °) l /a seems to represejlt the connexion between deviation and **wavelength** with considerable accuracy for prisms constructed with the ordinary media.

This fact has been employed for separating waves of large **wavelength**, and in this way waves of length 0 .

As, however, the **wavelength** necessary to cover any considerable distance must be at least 200 or 300 ft., it becomes impracticable to employ mirrors for reflection.

It is closely related to the coefficient k which we have just defined, the equation connecting the two being k= 4lrK/X,X being the **wavelength** of the incident light.

- Variation of energy of radiation corresponding to **wavelength** 30 µ, with temperature of source.

3 The power of a grating to construct light of nearly definite **wavelength** is well illustrated by Young's comparison with the production of a musical note by reflection of a sudden sound from a row of palings.

His remarkable result that two waves give some sense of pitch, in fact a tone with **wavelength** equal to the interval between the waves, has been confirmed by other observers.

The relative increase of index takes place on the side where the **wavelength** is greater than that of the absorbing system.

The refractive index of any substance varies with (1) the **wavelength** of the light; (2) with temperature; and (3) with the state of aggregation.

Half a **wavelength**, the frequency in the air is U/2L, where U is the velocity of sound in the pipe.

In general, we may say that aberration is unimportant when it nowhere (or at any rate over a relatively small area only) exceeds a small fraction of the **wavelength** (X).

In so far as the vibrations may be regarded as isochronous, the distance between consecutive corresponding points of the recurrent figure, or, as it may be called, the **wavelength** of the figure, is directly proportional to the velocity of the jet, i.e.