» by Chemical Action. J 1 3 



that of universal gravitation, has exhibited all the aspect of a 

 great physical fact, advancing to the explanation of things that 

 seemed to have no necessary connexion with it, and convertino- 

 what at first sight was regarded as contradictory into the firm- 

 est arguments for its truth. 



VIII. On the physical cause of Fraunhofer^s dark lines. 



Although I have extended this memoir to so great a lencth, 

 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 Fraun- 

 hofer's fixed lines. 



It has already been related how I was led to expect the 

 production of these lines in the flame of cyanogen, from con- 

 sidering the circumstances under which its combustion takes 

 place. Returning to this phaenomenon, I shall here point out 

 a very remarkable numerical relation existing among the fixed 

 lines of the solar spectrum. 



The following table contains Fraunhofer's determination 

 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 isoave-lengths correspo7iding to the eight great fixed 

 lines of the solar spectrum, the Paris inch being supposed to 

 be divided into one hundred millions of equal parts. 



A = 2660 

 B = 2541 

 C = 2422 

 D = 2175 

 E = 1945 

 F = 1794 

 G = 1587 

 H = 1464 



An examination of this table proves that 



the wave length of B is 119 parts less than A 



C 238 



D 485 



E 715 



F 866 



G 1073 



H 1196 



and these differences of length are obviously very nearly as 

 the whole numbers 1, 2, 4, 6, 7, 9, 10. This coincidence is 

 Phil. Mag. S. 3 . Vol . 32. No. 213. Feb. 1848. I 



