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

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.

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

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).

'; To obtain such it would be necessary that the retardation should gradually alter by a **wavelength** in passing over any element of the grating, and then fall back to its previous value, thus springing suddenly over a wave-length (Phil.

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.

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

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.

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

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.

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.

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