[ 144 ] 

 XVIII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 77>~\ 

 January 7, 1875. — Joseph Dalton Hooker, C.B., President, in the 



Chair. 

 riVHE following papers were read : — 



JL " Remarks on a New Map of the Solar Spectrum." By J. 

 Norman Lockyer, E.R.S. 



I beg permission to lay before the Royal Society a portion of the 

 new map of the solar spectrum referred to in one of my former 

 communications . 



It consists of the portion between w.l. 39 and 41. 



I have found it necessary, in order to include all the lines visible 

 in my photographs in such a manner that coincidences may be 



clearly shown, to construct it on four times the scale of Angstrom's 

 " Spectre Normal." 



The spectra of the following elements have been photographed 

 side by side with the solar spectrum and the coincidences shown : — 

 Ee, Co, Ni, Mn, Ce, U, Cr, Ba, Sr, Ca, K, Al. 



The wave-lengths of new lines in the portion of this spectrum 

 at present completed have been obtained from curves [of graphical 

 interpolation. Instead of the reading of a micrometer-scale, a pho- 

 tographic print of the spectrum has been employed in the con- 

 struction of these curves, the wave-lengths of the principal lines 

 being taken from an unpublished map of the ultra-violet region of 

 the solar spectrum, a copy of which has been kindly placed at my 

 disposal by M. Cornu. The photograph of the solar spectrum from 

 the ultra-violet to beyond E, kindly given to me by Mr. Rutherfurd, 

 has also proved of great service in the present work. I have, in fact, 

 up to the present time, only been able to excel this photograph in 

 the region about H. 



Erom the extreme difficulty of carrying on eye-observations 



upon the portion of the spectrum now completed, Angstrom's map 

 is, of course, very incomplete about this region. The few lines 

 mapped differ slightly in some cases from the positions assigned by 

 Cornu ; but the wave-lengths given by the latter observer generally 

 fall into the curve without breaking its symmetry, and these posi- 

 tions have therefore been adopted. The advantage possessed by 

 the photographic method over eye-observation may be estimated 

 from the following numerical comparisons : — 



Region of spectrum, 3900-4100. 

 Number of lines in Angstrom's " Spectre Normal " 39 



„ „ Angstrom's and Thale'n's map of the 



violet part of the solar spectrum .... 185 



„ ,, Cornu's map 205 



,, „ new map . . , 518 



