THE 



LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



SUPPLEMENT to VOL. XXIX. FOURTH SERIES. 



LXVIL On a new Determination of the Lengths of Waves of 

 Light, and on a Method of determining } by o Optics, the Trans- 

 lator!/ Motion of the Solar System, By A. J. Angstrom*. 

 [With a Plate.] 

 I. 



IN the Note on Fraunhofer' s lines which I had the honour of 

 communicating to the Royal Academy in October 1861, I 

 spoke of my intention of revising the lengths of luminous waves, 

 as determined by Fraunhoferf, and of extending these deter- 

 minations to all the remarkable lines of the spectrum, in order 

 with their help to obtain the wave-lengths for the metal-spectra. 



The weather last summer was, on the whole, scarcely favour- 

 able to such experiments on the solar spectrum, nor are these 

 experiments by any means complete. Nevertheless, since my 

 measurements of the principal lines of Fraunhofer are sufficiently 

 numerous and self-accordant to secure my results from any 

 essential change, I have deemed it of some interest to examine 

 whether, and to what extent, these new determinations agree 

 with those obtained by Fraunhofer himself — the more so because 

 no new measurements on the wave-lengths of light have, to my 

 knowledge, been made since Fraunhofer closed his wonderful 

 investigations. 



I employed in my experiments an optical theodolite constructed 

 by Pistor and Martins in Berlin, and a glass grating made by 

 the optician Nobert in Barth. The theodolite was provided with 

 two telescopes, the second of which served as a sight-indicator 

 (Sehzeichen). In reading off, two microscopes were used, and one 

 division of the micrometer corresponded to an angle of 2"'l. 



The eyepiece is also provided with a micrometer arrangement : 

 the screw-head is divided into 100 parts; and when the telescope 



* From PoggendorfFs Annalen, vol. cxxiii. p. 489 ; to which journal the 

 paper was communicated by the Author after its publication in the Oefver- 

 igt afK. Vet. Akad. Fork. 1863, No. 2. 

 t Poggendorff's Annalen, vol. cxvii. p. 290. 



Phil Mag. S. 4. No. 199. Suppl. Vol. 29. 2 K 



