LITTLE b GROUP OF LINES IN THE SOLAR SPECTRUM. 43 



in the present day. For as this Note must have shown, if it has shown anything, 

 the most radical and fundamental questions in all Chemistry and the very 

 constitution of the Cosmos depend upon the most recently elicited and minutest 

 of all the phenomena yet observed. 



P.S. September 28, 1883. 



The above position will become still more distinct on considering two sets of first rate observations in tbis 

 part of the Spectrum, contained in tbe Proceedings of the Royal Society (London), and the present paper should 

 by no means be allowed to close without honourable mention of both of them. 



The first to be noticed of these sets, is by Professors Liveing and Dewar, working in the magnificent 

 Cavendish Laboratory at Cambridge ; and writing at p. 229 of said Proceedings for May 1881, of b 3 , that it is 

 " a close double, but the Iron is less refrangible than the Nickel, line." 



While of i 4 they state with greater fulness :— 



" By examining the arc of a battery of 40 Grove cells, or that of a Siemens' machine, taken in a crucible of 

 lime under the dispersion of the spectrum of the fourth order given by a Eutherfurd grating of 17,296 lines 

 to the inch we are able to separate the iron and magnesium lines which form the very close pair ¥ of the solar 

 spectrum. Either of the two lines can be rendered the more prominent of the pair at will, by introducing iron 

 or magnesium into the crucible. The less refrangible line of the pair is thus seen to be due to iron, the more 

 refrangible to rnaonesium. Comparison of the solar line and the spark between magnesium points confirms 

 this conclusion, that the magnesium line is the more refrangible of the two." 



This accords well enough with, and indeed overshadows, my imperfect experiments in Edinburgh. But 

 what are we to think, on turning to p. 443 of the same Society's Proceedings for the earlier date of March 20, 

 1879 where that distinguished spectroscopist Mr Norman Lockyer, working with all the resources of the 

 Government Department of Science and Art at South Kensington, implies, of ft 3 , that there is no Iron there, 

 only Nickel ; but of ¥, that there are besides Iron and Magnesium, no less than 9 other metals, viz., Mo, W, Co, 

 Mn, Ca, Li'?, Na 1 ?, Cu, and Al, coincident with it. 



The beginning of some explanation of this difference undoubtedly is, that at the time of his observation, 

 the accomplished observer had not heard that both 6 3 and ¥ were double lines, and had not a spectroscope of 

 sufficient power to show them so. 



The second part of the explanation is probably due to the admission in the last par. of p. 442, that 

 compulsory "rapid surveys of tbe arc spectra of most of the metallic elements" have led to approximate, being 

 sometimes assumed as exact, coincidences. 



This is an almost necessary feature in the earlier stages of any inquiry ; but now that we are happy to 

 learn on one side, that Mr Lockyer has come into possession of one of Professor Bowland's (U.S.Am.) grand 

 concave Gratings, and on the other, know that the Natural Philosophy Laboratory of the Edinburgh University 

 possesses the Monckhoven-Cooke Spectroscope, together with a 4-horse power Gas-engine, Dynamo, Grand 

 Induction-Coil and Condenser to suit, — we may expect something very important from either one or both those 

 parties revising that list of so many metals supposed, four years ago, to have one common meeting place 

 in the Spectrum. 



C. P. S. 



EXPLANATION OF THE PLATE REPRESENTING THE COURSE OF DISCOVERY 

 TOUCHING: THE LITTLE i GROUP IN THE SOLAR SPECTRUM. 



This plate is rough and rude to a degree, and that is partly intended ; because, to attempt 

 to reproduce the infinite refinement of shades, tints and lines shown by Nature in the Solar 

 spectrum, belongs more to the department of artistic beauty, than scientific work ; and already 

 every high Solar scientist has utterly discarded the trouble and expense of introducing that 

 leading element of the Spectrum's beauty, colour, into his maps ; and has taken that very 

 stron^ step towards a symbolic, rather than realistic, representation, partly on account of the 

 absence of colour-pigments from his paper enabling him to bring out the more useful black or 

 grey of the Fraunhofer lines with greater force and more ease of recognition. 



But even then, in mere black and white, the question comes up once again, should we 

 attempt to reproduce every such refinement the spectrum itself shows, and in the manner in 

 which it appears there, — which would necessitate the most ultra microscopic engraving on 



