PLANET SATURN. ^fff 



I Viewed Jupiter, and compared its figure with that of 

 Saturn. An evident difference in the formation of the 

 two planets is visible. To distinguish the figure of Jupi- 

 ter properly it may be called an ellipsoid, and that of 

 Saturn a spheroid. 



Observations on the periodical Changes of the Colour of 



the polar Regions of Saturn. 



•In "the observations I have given on the planet Mars, probability 



it has been shoWn that an alternate periodical change that The polar 



tafcfss place in the extent and brightness of the north and f^S'ons ^i Sa- 

 ii 1 ^ ,T , , , ., turnarcfroaen. 



south polar spots *5 and 1 have there suggested an idea 



that the cause of the brightness might be a vivid reflec- 

 tion of light from frozen regions, and that the reduction 

 of the spots might be ascribed to their being exposed to 

 the sun. 



The following observations, I believe, will cither lead 

 us to similar conclusions with respect to the appearance 

 of the polar regions of Saturn, or will at least draw the 

 attention of future observers to a farther investigation of 

 the subject. 



With high magnify^g powers, the objects we observe Useful appHca- 

 require more light than when the power is lower; this ^^on of high 

 affords us a good method of determining the relative termine the re- 

 brightness of the different parts of a planet. The less lative bright- 

 bright object will be found deficient in illumination when "*^" ° objects, 

 the power exceeds what it will bear with ease. I have 

 availed myself of this assistance id the observations that 

 follow. 



June 25, 1781. With an aperture of 6,3 inches I Observations 

 used a magnifying power of 460. This gave a kind of °" ^^^ appear- 

 yellowish colour to the planet Saturn, while the ring and its rmg, 

 still retained its full white illumination. .partial changes 



November 11, 1793. From the quintuple belt toward ^f^^"S^»'»««» 

 the south pole the whole distance is of a pale whitish co- 

 lour; less bright than the white belts, and much less 

 bright than the ring. 



This has been represented in a figure which was given. 

 in the volume of the Phil. Trans, for 1794, page 32. It ' 



* Phil. Trans, for 1 784, page 260. 

 Vol. XV. — Supplement. H h h js 



