LITTLE b GROUP OF LINES IN THE SOLAR SPECTRUM. 39 



extensive knowledge implicit respect has hitherto been generally paid, have not 

 yet taken any notice of either M. Eievez or the American observers. A 

 particular case of such neglect is to be found in the new, or third edition, of 

 Dr Schellen's German work on " Spectrum Analysis " published during the 

 present year, 1883, in 2 volumes, and an atlas filled with excellent engravings. 



The number of different spectroscopes illustrated in those volumes is legion. 

 But amongst them all, the highest opinion seems to be entertained for the 

 spectroscope of Professor Vogel, already alluded to. The instrument was 

 made by the celebrated M. Schroder of Berlin, contains 6 large compound 

 prisms of heavy glass, with powerful telescope, collimator and automatic move- 

 ments to match. It is represented accordingly with pride in three pictures on 

 pp. 243, 244 and 245 ; while on p. 247, to prove beyond doubt how advanced 

 are its powers, a pair of diagrams of the little b group are given ; first, as 

 they were represented by Angstrom in his day ; and second, as they are 

 now seen by Professor Vogel. But though the latter, as I have already stated, 

 introduces several more thin lines, he leaves the four classic members of the 

 little b group, as given by Angstrom at the early spectroscopic date of 1868, 

 untouched ; for Dr Schellen, by some inadvertence having imparted haze to 

 Angstrom's view of 6 4 , has destroyed (on his own plate) the rightful claim 

 of Professor Vogel to that physical discovery. 



Now let us contrast that state of things with some observations I have just 

 been able to make in Edinburgh through the sunshine there, all smoky as it 

 unhappily is, at No. 15 Koyal Terrace, but Avith an admirable spectroscope, kindly 

 left in my hands for a few weeks by Professor P. G. Tait, — after he had, by a 

 marvellous chance, been able to acquire it for the Natural Philosophy Labora- 

 tory of the Edinburgh University. It is of English make, by Messrs T. Cooke 

 & Sons of York, but constructed for the late eminent Belgian scientist, Dr Van 

 Monckhoven, on a plan arranged between himself, Mr Lockyer and Messrs 

 Cooke ; though he had hardly received it when sudden death by angina pectoris 

 cut short his splendidly energetic and promising career, to the terrible grief of 

 his family and friends. The instrument thrown thus open to purchase again, 

 was sent here by Messrs Cooke, and I could not but admire exceedingly the 

 compactness of its arrangement, by which it was enabled in a remarkably small 

 compass and with absolute directness of vision throughout the whole spectrum, 

 to employ virtually any number of prisms from 2 to 20. Every prism too 

 being " simple," and of white flint glass ; a feature in happy opposition to the 

 compound prisms of brown or green flint glass, cemented to crown-glass anti- 

 prisms, which are far too frequent favourites elsewhere. 



But how did the Cooke spectroscope acquit itself, when tried with the 

 maximum number of its prisms, and highest magnifying power of eye piece ? 

 I was over and above delighted to find that it focussed more sharply than any 



