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VrU. Determinations of Wave-length from Spectra Obtained at the Total Solar 
Eclipses of 1900, 1901 and 1905. 
By Professor F. W. Dyson, M.A., F.R.S., Astronomer Royal for Scotland , Professor 
of Astronomy in the University of Edinburgh. (Member of the Expeditions 
from the Royal Observatory , Greenwich.) 
Deceived April 25,—Pmad May 17, 1906. 
[Plate 9.] 
The following paper consists of a discussion of the photographs of the spectra of 
the chromosphere and corona obtained in three eclipse expeditions from the Doyal 
Observatory, Greenwich. Preliminary reports of the expeditions of 1900 and 1905, 
where I was one of Sir William Christie’s party, are given in the ‘ Proceedings,’ 
vol. 67, p. 393, and A, vol. 77, p. 28, and a preliminary report of the expedition to 
Sumatra in 1901 is given by me in the ‘Proceedings,’ vol. 69, p. 235. For these 
eclipse expeditions two spectroscopes were kindly lent by Major Hills, the same 
spectroscopes he used for photographing the chromosphere and corona at the Indian 
eclipse of 1898. Deference is made in the preliminary reports to the large amount 
of assistance received by voluntary helpers in these expeditions; for special assistance 
in the spectrographic observations I am greatly indebted to Mr. J. J. Atkinson, 
Mr. Arthur Berry, and Captain Brett. The spectrograms were measured at the 
Doyal Observatory, Greenwich, by Mr. Davidson and myself, and I have profited by 
Mr. Davidson’s assistance and advice in the preliminary arrangement and adjustments 
of the spectroscopes as well as in the subsequent measurements and discussion. 
1. Details of the observations and of the adjustments of the spectroscopes are 
given in the ‘ Proceedings,’ vols. 67, 69, and 77. The following is a brief account of 
the spectrograms of the chromosphere measured :— 
Taken at Ovar, 1900, May 28. Second Contact. Slit a few minutes inside 
the Tangent to Limb. 
Flint Glass Spectroscope. —-Minimum deviation at H r 
(No. 6.) Spectrum consists entirely of bright lines and extends from (4862) to 
K (3933). Only 50 of the brightest lines are shown, 
VOL. ccvi. —a 409, 3 F 2 
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