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Page:Proceedings of the Royal Society of London Vol 60.djvu/193

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178
On the Determination of Wave-length of Electric Radiation.
The diameter of the central ball = 0·78 cm.
The diameter each side bead = 0·3  cm.
Distance between the outer surfaces of the beads = 1·5 cm.
Distance between inner (sparking) surfaces ,, = 0·9 cm.

The wave-length, 1·84, is almost exactly equal to twice the distance between the sparking surfaces of the beads. Without fnrther experiments with different sized radiators, it is difficult to say whether the above simple relation is accidental or not. The following rough determinations, made with a second radiator, may be of some interest in connexion with the above. I took off the central sphere from the radiator used in the last experiment, and substituted a larger ball. The distance between the inner sparking surfaces is then 1·2 cm.

Breadth of strip = 3 cm.
 i.  θ  λ  Mean.
 23·0°
29·0
34·5
 0°
–5
–10
 2·34
2·38
2·36
 2·36

The wave-length found is approximately equal to 2·36 cm., and twice the distance between the sparking surfaces is 2·40 cm.

Conclusion.—The experiments described above seem to prove that the diffracted spectrum is not continuous, but linear. The method of determining the wave-length of electric radiation by diffraction grating is seen to give results which are concordant. The determinations are not affected by the periodicity of the receiving circuit, the receiver being simply used as a radioscope. With a better mounting and a finely graduated circle, it would be possible to obtain results with a far greater degree of accuracy. I hope to send, in a future communication, the results obtained with a better form of apparatus, with which I intend to study the relation of the wave-length with the size of the radiator, and the influence of the enclosing tube on the wavelength. I shall at the same time send an account of transmission gratings.