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Page:Proceedings of the Royal Society of London Vol 60.djvu/192

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177
Wave-length of Electric Radiation by Diffraction Grating.
Grating B.—Breadth of strip = 1·5 cm.
 i.  θ  λ  Mean for B.
 38·0°
26·0
28·5
 0°
10
8
 1·847
1·836
1·849
 1·844

Grating C.—Breadth of strip = 2 cm.

 i.  θ  λ  Mean for C.
 27·5°
22·0
20·0
 0°
5
7
 1·846
1·847
1·855
 1·849

Grating D.—Breadth of strip = 2·5 cm.

 i.  θ  λ  Mean for D.
 21·5°
29·5
33·0
34·0
 0°
–7
–10
–11
 1·832
1·852
1·854
1·841
 1·845

Grating E.—Breadth of strip = 3 cm.

 i.  θ  λ  Mean for E.
 18·0°
23·25
25·5
31·0
 0°
–5
–7
–12
 1·854
1·845
1·851
1·843
 1·848

It would thus be seen that the different values of wave-length obtained from the above experiments are concordant, the mean value being 1·846 cm.

I then carefully removed the electrical vibrator, and measured approximately the size of the sparking balls. The radiator, it must be remembered, was placed vertically inside a square tube, each of whose sides is 2·5 cm. The radiator was about 1 cm. inside from the free end of the tube.