THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



JULY 1862. 

 I. On the Fraunhofer -lines visible in the Solar Spectrum. 







By A. J. Angstrom*. 



[With a Plate.] 



§1. [N a former memoir, " Optiska Undersokningar " (Op- 

 -L tical Researches), published by the Royal Academy 

 of Stockholm f, I have, for the purpose of illustrating the ab- 

 sorption of light, made use of a principle already propounded by 

 Euler in his " Theoria lucis et caloris," viz. that the particles of 

 a body, in consequence of resonance, absorb principally those 

 ethereal undulatory motions which have previously been im- 

 pressed upon them, and I extend the validity of this principle 

 not only to the case in which the absorbed light displays itself 

 sensibly as light and heat, but also to that in which its effect is 

 evidenced by chemical decomposition. Conversely, I endeavour 

 also to show that a body in a state of glowing heat emits just the 

 same kinds of light and heat which it absorbs under the same cir- 

 cumstances ; and it was in order to test the truth of this propo- 

 sition, and for that purpose to ascertain the different kinds of 

 light which different metals in a state of gaseous glow emit, that 

 the above-mentioned examination of the electric-light spectrum 

 was undertaken. 



The results at which I arrived in the above-named disquisition 

 were, in short, the following : — That the electrical spectrum, 

 which had been the especial object of the researches of Fraun- 

 hofer, Wheatstone, and Masson, must be considered as the 

 superposition of two spectra — the one belonging to the metal of 

 which the electrodes are made, the other to the gas through 



* Communicated by the Author, having been read before the Royal Aca- 

 demy of Science, Stockholm, Oct. 8, 1861. 



t Vet. Akad., Feb. 1853 (Philosophical Magazine, S. 4. vol. ix. p. 237). 



Phil Mag. S. 4. Vol. 24. No. 158. July 1 862. B 



