224 



Royal Society : — 



in 1864, we gave the results of our observations of the spectra of the 

 planets Venus, Mars, Jupiter, and Saturn ; but we found the light 

 from Uranus and Neptune too faint to be satisfactorily examined with 

 the spectroscope. 



By means of the equatorial refractor of 15 inches aperture, by 

 Messrs. Grubb and Son, recently placed in my hands by the Royal 

 Society, I have succeeded in making the observations described in 

 this paper of the remarkable spectrum which is afforded by the light 

 of the planet Uranus. 



It should be stated that the spectrum of Uranus was observed by 

 Father Secchi in 1869*. He says, " le jaune y fait completement 

 defaut. Dans le vert et dans le bleu il y a deux raies tres-larges et 

 tres-noires." He represents the band in the blue as more refrangible 

 than F, and the one in the green as near E. 



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C 



63 C6 



1 1 1 1 1 1 1 n 



The spectrum of Uranus, as it appears in my instrument, is repre- 

 sented in the accompanying diagram. The narrow spectrum placed 

 above that of Uranus gives the relative positions of the principal solar 

 lines and of the two strongest absorption-bands produced by our 

 atmosphere — namely, the group of lines a little more refrangible than 

 D, and the group which occurs about midway from C to D. The 

 scale placed above gives wave-lengths in millionths of a millimetre. • 



The spectrum of Uranus is continuous, without any part being 

 wanting, as far as the feebleness of its light permits it to be traced, 

 which is from about C to about G. 



On account of the small amount of light received from this planet, 

 I was not able to use a slit sufficiently narrow to bring out the 

 Fraunhofer lines. The positions of the bands produced by planetary 

 absorption, which are broad and strong in comparison with the solar 

 lines, were determined by the micrometer and by direct comparison 

 with the spectra of terrestrial substances. 



The spectroscope was furnished with one prism of dense flint- 

 glass, having a refracting- angle of 60°, an observing telescope mag- 

 nifying b\ diameters, and a collimator of 5 inches focal length. A 

 cylindrical lens was used to increase the breadth of the spectrum. 



The remarkable absorption taking place at Uranus shows itself 

 in six strong lines, which are drawn in the diagram. The least 



* Comptes Eendus, vol. lxyiii. p. 761, and ' Le Soleil,' Paris, 1870, p. 354. 



