250 On the Spectra of Argo and Orion, and of Jupiter. [Mar. 3, 



Jansen as special to aqueous vapour. An answer one way or the other 

 would he equally interesting ; for Mr. Huggins's observations and my own 

 later ones (which are indeed merely corroborative) go far to prove that, 

 whatever the cause of the lines, that which produces 914 and 838 has on 

 Jupiter more efficacy than that which produces 882, while the reverse 

 appears to be the case on the earth. 



Jupiter was taken in hand specially to note any peculiarity in the spec- 

 trum of different parts of the surface, as regards general or specific absorp- 

 tion. The best observations were made on the night of December 11th, 

 when the phenomena were as given in the diagram (Plate I. fig. 2), to 

 which the second figure of Jupiter is added merely for any additional 

 interest to be derived from two views on the same night (a at 9.30, b at 

 11.30+). 



The space N P is slightly yellowish, and appears at good defining mo- 

 ments to be crossed by a multitude of fine hair lines (this has been seen 

 more than once) ; P Q is white, and considerably brighter than the general 

 surface ; QR dusky yellow, much darker than N P ; RT white ; TS similar 

 to P Q, but more approaching to white. 



P, Q, R, T dark brown with occasional suspicion of green tinge. 



The spectrum, as given in the diagram, is an inversion (to suit telescopic 

 image of planet) of what is seen in the spectroscope with the slit perpendi- 

 cular to Jupiter's equator. 



The absorption of Q, R is most marked beyond F, fading gradually 

 away to about E ; beyond this Q, R are seen separately with an apparently 

 undiminished spectrum between them ; P Q is much brighter than the 

 general spectrum, and is normal throughout ; T R occasionally flashes out 

 brightly ; P stretches equally across the spectrum ; T is most marked at 

 the less refrangible end (the reverse of this was the case for one of the belts 

 on a former occasion). 



A special point aimed at in these observations was to note any peculiarity 

 in the lines 914, 838 as they cross the various parts of the surface in this 

 position of the slit, but no satisfactory evidence could be elicited. As 

 before mentioned, by the interposition of a suitable lens the image, still 

 focused on the slit, may be condensed at pleasure within certain limits ; a 

 point is therefore chosen at which the compromise between brilliancy of 

 spectrum and size of image is deemed most suitable for the object in view. 

 The light is quite adequate for the purpose when the bands T Q, Q R are 

 still of considerable width; any difference, if not very slight, in the line 914 

 as it crossed the different bands ought therefore to have been detected. 

 This was not the case. The experiment was tried of placing the slit 

 parallel to the bands, but with no new result. 

 Melbourne Observatory, January 3, 1870. 



