232 Photographic Spectra of Uranus and Saturn. [June 6, 



visible spectrum of this planet and its rings. In my paper on the 

 " Photographic Spectra of Stars,"* I described the photographic 

 spectra of Venus, Jupiter, and Mars. About a year later I took a 

 photograph of the spectrum of Saturn and his rings, but as it did not 

 present any new features, but was purely solar, I have not given any 

 description of it. 



The favourable position of Saturn this year for obtaining a photo- 

 graph in which the spectra of the ansae of the rings could be seen 

 distinct from the spectrum of the ball and of the part of the ring 

 crossing it, determined me to take some photographs of the planet 

 and its rings. 



I have adopted the plan described in 1880, in which the planet is 

 photographed while the sky is sufficiently bright to give a faint day- 

 light spectrum on the plate. Any additional lines or other modifica- 

 tions of solar light due to the planet's atmosphere can in this way 

 be easily detected. 



In the photographs taken this year the slit was so placed upon 

 Saturn that the spectrum consists of three distinct parts, the middle 

 part being formed by the light from the ball, and the part of the 

 ring across it, and on both sides of this spectrum the spectra of the ansae. 

 The planet was kept upon the same part of the slit with sufficient 

 exactness to keep these three spectra distinct, and from encroaching 

 upon each other, and therefore if any difference existed between them 

 it could be detected. 



The exact correspondence of the Fraunhofer lines in the spectrum 

 of the planet and its rings with those of the sky spectrum is clearly 

 shown, but I am unable now, as I was in 1881, to detect any lines, 

 dark or bright, other than those which are also present in the sky 

 spectra. The spectrum on the plate extends from a little above F to 

 beyond ~N in the ultra-violet. 



I am trying to obtain enlargements of the spectra of Saturn and 

 Uranus to serve as illustrations to this note. If they can be done so 

 as to admit of reproduction, I will do myself the honour to present 

 them to the Royal Society. 



[We have observed since, the visible spectrum of Uranus, but under 

 unfavourable conditions, the planet being low and the sky not dark. 

 These observations confirm me strongly in the opinion I formed in 

 1871 that the brighter parts of the spectrum appear so as an effect of 

 contrast, and do not represent emitted light. In the moments of 

 best vision the spectrum on both sides of the brighter parts appeared 

 to be darkened by groups of lines which give a heightened effect by 

 contrast to the less obscured parts between them. 



* ' Phil. Trans.,' 1880, p. 669. 



