Royal Society. 145 



It will serve further to illustrate the advantages of the photo- 

 graphic method, to compare the number of lines in the spectra of 

 metals already observed with the number of lines of the same metal 



given by Angstrom in the " Spectre Normal." 



Region of spectrum, 3900-4100. 



Metal. 

 Fe.. 



Lines 



in new map. 



71 



Lines in Thalen's map. 

 19 



Mn 



53 





, 12 



Co 



47 ... 







M, . 



17 







Ce.. 



163 







U .. 



18 .. . 







Or.. 



24 







Ba 



7 ... 







Sr . . 



5 . . . 







Ca 



7 ... 





6 



K .. 



Total.. .. 



2 ... 







Al.. 



2 





2 





416 



Total.. .. 



39 



The purification of the various metallic spectra has at present 

 been only partially effected ; but I have seen enough already to 

 convince me of the extreme rigour with which the principle I have 

 already announced may be applied, while, at the same time, there 

 are evidences that the application of it may lead to some results 

 not anticipated in the first instance. 



My object in laying these maps before the Society, and present- 

 ing this ad interim report of progress, is to appeal to some other 

 man of science, if not in England, then in some other country, to 

 come forward to aid in the work, which it is improbable that I, 

 with my small observational means and limited time, can carry 

 to a termination. I reckon that, having regard to routine solar 

 work, it will require another year before the portion from H to G 

 is completely finished, even for the metals the spectra of which are 

 shown in the maps now exhibited. When this is done there will 

 still remain outstanding all the ultra-violet portion, the portion 

 from G- to P (both capable of being photographed by short expo- 

 sure), and the whole of the less-refrangible part (which both Draper 

 and Eutherfurd have shown can be reached by long exposure 

 with the present processes). 



I cannot but think, moreover, that when the light which the 

 spectroscope has already thrown upon molecular action shall be 

 better known, and used as a basis for further inquiry, methods of 

 photography greatly exceeding the present one in rapidity, in the 

 less-refrangible portion of the spectrum, will be developed and 

 utilized in the research. 



The map is being drawn by my assistant, Mr. Raphael Meldola 

 (to whom my thanks are due for the skill and patience he has 



Phil. Mag. S. 4. Vol. 50. No. 329. Aug. 1875. L 



