508 Mr. J. N. Lockyer on Spectrum- Analysis. [Nov. 27, 



placed on its homogeneity. The paper is accompanied by a series of four 

 curves, which show the results of experiments, and in which the 

 coordinates are given by the ordinary method of assay, and by the spec- 

 troscopic readings. 



The chief practical advantage which appeared to flow from this inquiry 

 was that, if it were possible to replace the parting assay by the spectro- 

 scopical method, a great saving of time in ascertaining the value of gold 

 bullion would be effected. 



III. " Researches in Spectrum- Analysis in connexion with the Spec- 

 trum of the Sun." — Part III. By J. Norman Lockyer. 

 Received November 20, 1873. 



(Abstract.) 



The paper commences with an introduction, in which the general line 

 of work since the last paper is indicated. Roughly speaking, this has 

 been to ascertain the capabilities of the new method in a quantitative 

 direction. It is stated that while qualitative spectrum-analysis depends 

 upon the positions of the lines, quantitative spectrum-analysis on the 

 other hand depends not on position but on the length, brightness, and 

 thickness of the lines. 



The necessity of maps carefully executed and showing the individu- 

 ality of each line is shown ; and it is stated that the execution of these 

 maps required the use of the electric arc to render the vapours of the 

 metals incandescent. A battery of 30 Grove's cells of one pint capacity 

 was accordingly employed in the researches about to be described. 



The difficulties of eye-observations of the characters of the lines 

 compelled the application of photography, another reason for the use of 

 which existed in the facility it afforded for confronting spectra with each 

 other, and so eliminating coincident lines, since the lines, if due to im- 

 purities, would be longest and thickest in the spectrum to which they 

 really belonged. 



The portion of the spectrum at present worked upon is that from H 

 toF. 



Another branch of the research has been the construction of a Table of 

 all the named Fraunhofer lines, showing the lengths and thicknesses of the 

 metallic lines to the absorption of which they were due ; this Table enabled 

 the author to allocate upwards of 50 lines in the solar spectrum, pre- 



O" _ - 



sumably overlooked by Angstrom and Thalen. The Table was intended 

 as a preliminary to a new photographic map of the spectrum from H to F, 



o 



on a larger scale than Angstrom's, which was intended to clear away all 

 the difficulties touching coincidences — and to have below it complete maps 

 of all the solar elements with their long and short lines. This map is in- 

 complete at present, but is making rapid progress. 



