On the Production of Light by Chemical Action. 171 
ductive Sciences ;—how this theory, like that of universal gravi- 
tation, has exhibited all the aspect of a great physical fact, advan- 
cing to the explanation of things that seemed to have no neces- 
sary connexion with it, and converting what at first sight was 
regarded as contradictory, into the firmest arguments for its truth. 
VIII. On the physical cause of F'raunhofer’s dark lines. 
Although I have extended this memoir to so great a length, I 
have omitted many facts which have been made the subject of 
experiment. I cannot however conclude without offering some 
remarks on the artificial production and cause of Fraunhofer’s 
fixed lines. 
It has already been related how I was led to expect the pro- 
duction of these lines in the flame of cyanogen from considering 
the circumstances under which its combustion takes place. Re- 
turning to this phenomenon, I shall here point out a very remark- 
able numerical relation existing among the fixed lines of the 
solar spectrum. 
_ The following table contains Fraunhofer’s determinations of 
the wave lengths corresponding to the seven great fixed lines of 
the spectrum, which are designated by the capital letters of the 
alphabet from B to H. I have added the wave length of A from 
my own experiments. 
Table of wave lengths, corresponding to the eight great fixed lines of the solar spec- 
trum ; the Paris inch being supposed to be divided into one hundred millions of 
equal parts : 
A = 2660 E = 1945 
B = 2541 F = 1794 
C = 2422 G = 1587 
D = 2175 H = 1464 
An examination of this table proves, 
the length of B is 119 parts less than A. 
“ce “e Cc “ 938 “és ee “ ‘ 
ii4 +4 D “c A485 cc “cc “cc “ 
cc cc E <4 715 ce “ “ec iT4 
6c “ce “ 866 iia “se ce “é 
6 3 H “1196 “ £6. at “ 
and these differences of length are obviously very nearly as the 
whole numbers 1, 2, 4, 6, 7, 9, 10. ‘This coincidence is far too 
striking to be merely accidental. Moreover, it must not be for- 
gotten, that the observed numbers as determined by Fraunhofer 
are wholly independent of any hypothesis. 
If the relation of whole numbers was rigorously true, the 
numbers in the foregoing table would stand as follows: 119, 238, 
476, 714, 833, 1071, 1199. 38 ; 
_ The wave length of the most luminous portion of the spec- 
um, the centre of the yellow space, is 2060 parts. If we take 
Srconp Serres, Vol. V, No. 14.—March, 1848. 23 
