1889.] Photographic Spectra of Uranus and Saturn. 



231 



VII. " Note on the Photographic Spectra of Uranus and Saturn." 

 By William Huggins, D.C.L., LL.D., F.R.S., and Mrs. 

 Huggins. Received June 5, 1889. 



Uranus. — In 1871 I had the honour to communicate to the Royal 

 Society an account of the examination of the visible spectrum of 

 Uranus.* The visible spectrum of this planet is remarkable, as it is 

 seen to be crossed by several strong lines of absorption. Six of these 

 dark bands are shown in a diagram which accompanies the paper, and 

 their approximate positions in the spectrum are given. The spaces 

 between the dark bands appear bright by contrast, and might suggest at 

 first sight bright bands. I was unable to use a slit sufficiently narrow 

 to enable me to determine whether the bright parts of the spectrum 

 contain the Fraunhofer lines, which would be the case if Uranus, 

 like the other planets, shines by reflected solar light. 



The spectrum of this planet was carefully examined in 1872 by 

 Vogel,f whose results are in accordance with my earlier ones. He 

 observed some fainter lines or bands, in addition to those given in my 

 paper. Yogel was unable to obtain evidence of the Fraunhofer lines. 

 His observations agree with mine in placing a dark band at the 

 position of F in the solar spectrum. J 



In consequence of the Fraunhofer lines not having been seen, a 

 presumption has arisen that Uranus may shine, in part at least, by 

 emitted light. 



It appeared to me that this question might be answered by 

 photography. With an exposure of two hours, I obtained on June 3 

 a photograph of the spectrum of the planet from a little above F to 

 beyond N in the ultra-violet. A pair of sky spectra, one on each side 

 of the planet's spectrum, were taken on the same plate. 



The spectrum of Uranus, though fainter, shows all the chief 

 Fraunhofer lines seen in the comparison spectra, and is clearly solar. 

 I have not been able to detect any indications of bright lines, nor of 

 any strong bands or groups of absorption, such as those in its spectrum 

 from F to C. 



There can be no doubt that the spectrum of Uranus, at least, 

 from a little above F to 'beyond N in the ultra-violet, is due to 

 reflected solar light. I have not yet been able to re-examine the 

 visible spectrum of the planet. 



Saturn. — In 1864, I gave an account of an examination of the 



* 1 Eoy. Soe. Proc.,' vol. 19, p. 488. 



t 1 Untersuchungen iiber die Spectra der Planeteti,' Leipzig, 1874. 

 X Measures of some of the bands were made at Greenwich in 1882. See ' Green- 

 wich Spectroscopic and Photographic Eesults,' 1882, p. 33 . 



