250 REPORT— 1873. 



method of direct superposition upon the solar spectrum is in a forward state. 

 The solar lines have been thrown into the groups which catch the eye in ob- 

 serving the spectrum ; and the position of each line has been corrected for the 



dispersion of the air. Both Kirchhoff s arbitrary number and Angstrom's 

 determination of wave-length will be given along with the wave-number for 

 each line ; so that it is hoped that, when these catalogues are printed, ob- 

 servers will find in them, in a collected form, the best materials which yet 

 exist for the identification of lines, and for reducing fresh determinations, 

 either to wave-lengths in air or wave-numbers in vacuo. 



The Committee had taken Angstrom's determinations of the wave-lengths 

 of about a thousand solar lines, published in his ' Recherclies sur lo Spectre 

 Solaii'e,' as the foundation of their catalogues. They are therefore glad to 

 "be able to state, on the authority of the Astronomer lioyal, that his criticism 



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of Angstrom's labours in the Philosophical Transactions for 1872, pp. 90 



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ife 109, refers to preliminary measures made by Angstrom in 1863 mth im- 

 perfect apparatus, and does not aficct the determinations which have been 

 relied on by the Committee. ^ 



The small final coiTcctions mentioned by Angstrom at p. 29 of his memoir 

 have been applied throughout to the numbers of his catalogue. The correc- 

 tion for each line was ascertained by a diagram constructed by plotting 

 down the corrections corresponding to the lines of the select list which he 

 gives on pp. 31 & 32. The Association Catalogue may therefore be regarded 



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as representing Angstrom's work in its finished state. 



The corrections to be applied for the dispersion of the air have been 

 deduced from Ketteler's determinations of the refractive inthces of air cor- 

 responding to the positions of the lithium, sodium, and thallium lines. These 

 give only three points on the curve ; but as they lie nearly in a straight line 

 when referred to a scale of wave-niimbers, the extension to the limits of the 

 visible spectrum is tolerably safe. jSTevertheless it would be very desirable 

 that a determination of this important correction should be made, extending 

 over the whole spectrum. One of the members of the Committee hoped to 

 execute this work, and planned the apparatus which seemed necessary ; but 

 he could not command sufficient time to carry out his intention. 



Since your Committee have not finished the task intrusted to them, they 

 recommend that they be reappointed ; they would request that Messrs. Spot- 

 tiswoode and Do La Eue be invited to serve along with them. 



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Rejjort of the Committee, consisting of ^'ix John Lubbock, Bart., Pro- 

 • lessor Phillips^ Professor Hughes, and W. Eoyd Daavkins, Secre- 

 tary, appointed for the purpose of exploring the Settle Caves. 

 Drawn up by Mr. Boyd Dawkins. 



The Committee appointed by the British A.ssociation at the last Meeting, 

 at Brighton, to cooperate with the Settle-Cave Committee in carrying on the 

 exploration of the Victoria Cave, has expended the grant intrusted to them, 

 with but negative results. Since the last Eeport was pubhshed, in which 

 the discovery of the Pleistocene cave- earth underneath the grey clay at the 

 entrance was recorded, their attention was directed to the examination of the 



