VISUAL, GRATING AND GLASS-LENS, SOLAR SPECTRUM. 543 



fraught with a further degree of close set lines and linelets ; following, 

 apparently, in each of the three cases, certain harmonic variations of one 

 fundamental idea ; and that not of the uniformity of an iron railing and its 

 mere equal spaces, but with a delicate rise and fall of proportions most 

 intensely admired by those of artistic mind. Wherefore every good observer, 

 can hardly but regard with almost solemn awe, this surpassing and aesthetic 

 symmetry of elemental matter, which is obeyed so perfectly by every vibrating 

 atom of a given element, but remains at present beyond all human mathematical 

 theory to equal or explain. 



Now if we measure these groups on a Wave-length scale they give, as on 

 my original instrumental records, — 



Great A =23'86 inches, 

 Great B =18 - 40 inches, and 

 Alpha band = 14 - 98 inches ; 



or with most violent variations of size and a converging tendency, threatening- 

 compression amounting to practical extinction and invisibility in the much 

 further blue, and violet, regions of the Spectrum. Regions too where every 

 observer knows so well, that more map space than what the " Wave-length " 

 can give, is so imperatively required to do simple justice to the increased 

 number of lines that appear there, as compared with the Orange and Yellow 

 domains. 



But if we now measure the three Oxygen repetitions on a Wave-number 

 scale (or practically the same as the Oscillation frequencies, so long advo- 

 cated, but now at the last moment rejected, by the British Association), they 

 come out thus, on the final plates herewith presented to the Royal Society, 

 Edinburgh, viz. : — 



Great A =9*24 inches, 

 Great B =9-00 inches, 

 Alpha band = 920 inches. 



So that, as a natural representation, and in accord with the latest dis- 

 coveries of both Solar and chemical spectra, there is not at present known any 

 better scale than that which has been employed, for already published good 

 physical reasons, throughout the 60 plates of this paper on " The Solar (grating 

 and glass-lens) visual Spectrum in 1884." And these plates themselves now 

 follow, — with their naturally expanded room for Blue, Violet and Ultra-violet, 

 lines, — to aid quick and easy examination of their multitudinous natural features, 

 which consist as often in the grouping of many close lines, as in the absolute 

 place of one standing solitary by itself. 



Part IX. — The Map in 60 Plates, and with an Index Plate. 



VOL. XXXII. PAKT III. 4 u 



