38 C. PIAZZI SMYTH ON THE 



there is a picture by Sir David Brewster and Dr Gladstone confirming these 

 four grand lines of little b, and adding some thinner intervening lines and faint 

 broad bands. But before that could produce much effect on men's minds, it 

 was utterly eclipsed by the far grander Solar Spectrum map, first of Prof. 

 Kirchoff, and then of Professor Angstrom, whose exquisitely engraved, and 

 certified, map still remains for many purposes the Normal Solar Spectrum Map 

 of all the human race. 



Now let us take a new start from that last map, date 1868, in order to 

 ascertain something of our present degree of knowledge touching the visible 

 characteristics of these four remarkable lines ; for however many thinner ones 

 there may be, the principal members of the group are four only, and have over- 

 whelming importance. Two of these moreover, viz., b 1 and b 2 were represented 

 by Angstrom physically different from the others, by slightly bordering them 

 with haze. 



In 1875 the Royal Society published a map in their Philosophical Transac- 

 tions, where they represented (though by a very exceptional kind of symbolic 

 marking, looking really like something else very different but very important if 

 true) these haze borders of b 1 and b 2 as still broader ; but made 6 3 and b i , pale 

 in a high, dark in a low, sun, as though they were atmospheric or telluric lines, 

 which they certainly are not. 



In 1880 M. Fievez, in the R. Observatory of Brussels, represented several 

 lines hazy, though he left £ 4 quite sharp and black. 



But in the same year Professor Vogel, of the Astro-Physicalischen Observa- 

 tory at Potsdam in Prussia, and armed with a new spectroscope of immense 

 power, published a very superior spectrum map wherein he represented b l , 6 2 

 and ¥ all equally and very broadly hazy, but kept b B quite sharp, well defined 

 and black, besides adding many thin lines, some single and others double. 



In the following year at Madeira I had the opportunity, besides confirming 

 Professor Vogel on all the four great lines, of adding thereto the further physi- 

 cal distinction that the lines themselves, inside the envelopes of haze of b 1 , b 2 

 and £> 4 were all of a peculiarly faint material ; and of presently still further 

 discovering both that the & 4 line, within the compass of its own haze, was 

 double ; and that 6 3 , without any haze, appeared not actually double, but to 

 promise certain resolvability into it, had my apparatus been only of a slightly 

 better order. 



At the time I could hardly believe my eyes ; but have learned since then 

 that the duplicities of 6 3 and 6 4 had been just previously to that date ascer- 

 tained with some of the splendid spectroscopes in America ; as they were also 

 subsequently by a second very powerful spectroscope built up, and employed 

 by M. Fievez at the Royal Observatory, Brussels, in 1882. 



But perhaps I am going on too fast ; for certain learned parties, to whose 



