54 REPORT — 1872. 



Accordingly, your Committee decided on reducing to wave-numbers all the 

 wave-lengths, whether of solar lines or of the rays of incandescent vapours, 

 which have been determined with sufficient precision. Mr. Charles E. Burton 

 has offered his services gratuitously for making the necessary reductions, and 

 has made considerable progress with the solar spectrum, the greater part of 

 which is now nearly ready for the press. 



A specimen of the catalogue of solar lines is appended to this Eeport, 

 containing the lines from E to b. It is intended that this catalogue shall 

 contain in a compact form all the most useful information that is ^ available, 

 viz. : — References to the position of each line on Eirchhoff's and Angstrom's 

 maps, details of the process by which the standard wave-numbers have been 

 deduced, and indications of the intensitj', width, and origin of each ray 

 wherever these have been determined*. The rays will, moreover, be 

 bracketed into the groups which strike the eye in looking at the spectrum, 

 and a number will be assigned to each group which wUl sufficiently indicate 

 its position on the standard scale. 



Your Committee have as yet only incurred an expenditure of £4 for books, 

 maps, and preliminary printing. This leaves a balance of .£16 in their hands 

 out of the grant of £20 placed at their disposal last year. 



It is estimated that the two catalogues which the Committee propose to 

 publish (the Catalogue of the Principal Lines of the Solar Spectrum, and the 

 Catalogue of Rays of Incandescent Vapours) wUl cost about =£60. This does 

 not include the cost of the charts, which ought to accompany the catalogues 

 in order to render them complete. The charts would increase the entire sum 

 to be expended, including the grant already made, to about £120 ; but a 

 portion of this sum would return to the Association in the form of the pro- 

 ceeds from the sale of the catalogues and charts. 



Your Committee think that they could render the second catalogue more 

 perfect if they were in a position to employ a competent person to revise and 

 extend the determinations of the rays of incandescent vapours ; and they 

 therefore suggest that this revision be made a part of their functions, and 

 that an addition of £50 be made to the grant for this purpose. This woiild 

 increase the sum to be granted this year to £150. 



The Committee accordingly recommend that they be reappointed, and that 

 this sum be placed at their disposal, in addition to the balance at present in 

 their hands. 



Appendix. 



Sjjecimen of a Catalogue of the Principal BarJc Hays of the visible imrt of the 



Solar Spectrum, containing all the Rays registered by Kirchhoff and 



o 



Angstrom, arranged on a scale of Standard Wave-Numbers. (The Spe- 

 cimen contains the Rays from E to b). 



Column 1 gives the position on the Arbitrary Scale attached to KirchhoflTs 

 maps. 



Q Column 2 reproduces the wave-lengths in ^tenth metres as determined by 

 Angstrom, after applying to the numbers of Angstrom's list the small cor- 

 rections which he indicates at p. 29 of his memoir, " Le Spectre Normal du 

 Soleil." The wave-lengths of this list are wave-lengths in air of 760 millims. 

 pressure at Upsala, and 16° C. temperature. 



Column 3 contains the reciprocals of the numbers of Column 2, each mul- 



* Mr. Burton intends to revi.se the more refrangible part of the spectrum, and to supply 

 the intensities and widths of the lines of this portion, which was not included in KirchhoiTs 

 investigation. 



