Interferometric Measurements of Wave-Lenghts: I. Development of the Method of Channels and its Application at 5080 A and 6020 A

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Abstract
Collisional shifts are now known to contribute to the differences between solar and laboratory wave-lengths. In view of this, it is in practice essential to determine the absolute wave-lengths in each of the sources independently. Differences reaching as much as 0.010 A between the accepted earlier measures show that the absolute values of the solar wave-lengths, at least, have not yet reached the accuracy required for comparisons with theory. A new method of wave-length measurement has been developed, as suggested by Treanor in 1949. This method of “circular channels” enables solar and laboratory wave-lengths, in any spectral region, to be determined by direct comparison with the primary standard. The methods of observation, measurement and reduction are described in detail. In common with the usual method of “parabolic channels” particular attention has to be paid to the displacement of the centre of the interference pattern, the determination of the focal length of the camera lens, and the correction for phase change, all as functions of wave-length, as well as to departures from the “square law”. Measures have so far been made at 5080 A and 6020 A, for solar lines and corresponding lines in the vacuum arc. The “red shift” of the solar lines is 0.0093 A at 5080 A, but only 0.0065 A at 6020 A. These results cannot be explained as being due to a combination of the relativity shift (0.0107 A at 5080 A and 0.0126 A at 6020 A), with any reasonable collisional shifts.

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