Abstract
486 vacuum wavelengths of the thorium spectrum in the range 9050–2566 Å have been measured by comparison with the isotope Kr 86 line at 6057 Å, by using a reflecting echelon interferometer crossed externally with a Littrow spectrograph. Tests of accuracy by recurring interlevel differences indicate that the average error is about 1 in 107. Details are given of the sealed-off Schüler tube used as the thorium source. Difficulties which arose from the use of an Ebert spectrograph to photograph the spectrum are discussed.
© 1965 Optical Society of America
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