CALIFORNIA ACADEMY OF SCIENCES. 347 



diameter of the limb it was again seen as a dark spot. 

 Gradually it was lost to Mr. Hill and myself. 



It was next seen (8k. 30m.) as a minute button of light, 

 projecting outside the limb of the planet; but the atmos- 

 phere was very unsteady, and the moments of partial quiet 

 were very short. When the satellite was leaving the planet 

 and had become tangent to its limb (8h. 41m.), it appeared 

 lower than the prolonged line of its passage as a dark image 

 would have indicated; as if the dark image were nearer the 

 equatorial line of Jupiter and the bright image toward the 

 pole. Had I suspected such a result I should have pre- 

 pared instrumental tests to determine that. 



When the bright image of the satellite was clear of the 

 planet (8h. 44.5m.) it was not one-sixth as bright as Satellite 

 II, which was near for comparison; yet the brightness of 

 the planet must prevent an accurate judgment. Mr. Hill 

 thought it only one-tenth as bright as II. 



At times the image seemed a little above (apparently) the 

 line of the lower edge of the belt projected, but the atmos- 

 phere was very unsteady. 



At 9h. 01m. I had a good view. The Satellite IV was 

 only one-sixth as bright as Satellite II; and I feel sure that 

 it is apparently above the line of the lower edge of the belt 

 prolonged. 



Some drawings were made of the different phases above 

 indicated. 



A reasonable inference from the foregoing observations 

 is that the face of the satellite presented to the observer 

 was in part dark, and in part bright. A similar property in 

 the case of the III Satellite was clearly exhibited in my ob- 

 servations on January 15, 1884, when the bright and dark 

 spots of the image were visible at the same time projected 

 on the disk of the planet. 



