= 
THE SOLAR SPECTRUM AT THE DATE 1877-78. 341 
PP ie N-D I. X. 
While the above paper was passing through the Press, I have had the honour of receiving 
from Prof. S. P. LANGLEY, of the Alleghaney Observatory, United States, North America, a 
copy of his double pamphlet on, 1st, the Solar Spectral lines, A and B, Oct. 7, 1878; and 2nd, 
the Temperature of the Sun’s visible surface, Oct. 9, 1878; printed subsequently in the 
Proceedings of the American Academy. 
Prof. LANGLEY has, if I may presume so to say, a speciality for doing whatever he has to 
do, most thoroughly ; so that his one drawing of a Sun-spot a few years ago, copied into Padre 
SEccur’s classical work on the Sun, outweighs at once the legions of drawings by almost all 
the other observers put together; and in the present instance, his labours have not been of a 
less excelsior kind. 
Remembering, as I do, the sudden delight with which my Wife and I recognised the exquisite 
duplicity residing in the lines of great B and its preliminary band, when we first saw them in 
June, 1878,—I must congratulate Prof. LANGLEY on having been able to detect a similar duplicity 
in the lines composing the preliminary band of great A. I can believe it too, most completely, 
though I did not see it so myself; for the Dispersion at that point of the spectrum with the “ grat- 
ing” he used (the most magnificent example yet given forth of Mr RuTHERFORD’s unequalled 
mechanics, containing 17296 lines per inch, over a surface 1°75 inch square), must have been 
some three times greater, and much better defined too, than anything which could be got out of 
the small compound prisms to which I was restricted in my examinations of A and its band of 
lines in 1877. But the larger prisms which I used in 1878 on the B line, enabled me both to 
see and measure, not only the duplicity of the lines of B’s preliminary band, but of those of its 
attached band as well; a higher and more refined kind of duplicity, which does not seem to 
have been noted yet by any one else, and may be the subject of further observation. 
Next, with regard to the Temperature of the Sun’s photospheric surface, Prof. LANGLEY’s mode 
of proceeding was so different from mine,—that the very similar, though more positively and 
numerically expressed, conclusions which he arrives at finally, are a most satisfactory confirma- 
tion on a point of exceeding difficulty, but of infinite importance to man and all his science. 
Prof. LANGLEY first calls attention to the extravagant differences of result among many of 
the best scientists, and especially to their later lowerings of the Sun’s surface temperature,— 
so that while, a few years ago, that all important quantity was announced by,— 
Sir JOHN HERSCHEL, . ? é : ; = 9,000,000" Kahr 
And by Mr ErIcsseEn, F 5 : . = 4,000,000 . 
The late Padre SECCHI made it only, . ; P= 239,000 a 
Sir WILLIAM THOMSON and others, from : = 108/000 i 
down to : . = 54000, 
Several French observers, . ’ : , = 4,500 - 
And lastly, M. VioLtx, of Grenoble, only = 2,800 £ 
the latter figure being lower than that for melting platinum. 
VOL. XXIX. PART I. 4s 
