VOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. ] 89 



usual colour. — The 1st satellite is very bright, and its light is of the usual in- 

 tenseness. 



The magnitudes with 300. — The diameter of the 4th seems to be to that of the 

 3d, as 2 to 3 ; or perhaps more exactly, as 3 to 5. — The diameter of the 4 th satel- 

 lite exceeds that of the 1st a very little. — With 400. With this power the diameter 

 of the 4th satellite certainly exceeds that of the 1st. — The diameter of the 4th is 

 to that of the 3d, as 3 to 5. 



July 30, 1794, 19 h l m 37 s , 10-feet reflector; power 300: the 4th satellite of 

 Jupiter is a little larger than the 1st: it is of its usual colour. The 2d is less than 

 the 1st. The 3d is larger than the 4th. 



July 31, 1794, 17 h 18 m 38 s ; 10-feet reflector; power 17O: the 4 satellites of 

 Jupiter are very favourably placed for my purpose. The 1st is less bright than the 

 2d: it is a very little larger than the 2d: the difference in the size is but barely 

 visible. The light of the 2d is very intense and white. The light of the 3d is 

 very intense and bright. The light of the 4th is dull ; and seems to be inferior to 

 the usual proportion it bears to the other satellites. — At 18 h 38 m 38 s ; with 300; 

 the 4th satellite is larger than the 1st; the 2d satellite is a little larger than the 1st, 

 or at least equal to it; the 3d is undoubtedly the largest. The order of the mag- 

 nitudes therefore is, 3 4 2 1 . My brother, Alexander Herschel, looked at the sa- 

 tellites, and estimated the order of their magnitudes exactly the same; though he 

 was not present when I made the foregoing estimations. 



August 1, 1794, 17 h 38 m 37 s ; 10-feet reflector; power 170: the light of all 

 the 4 satellites is very brilliant, the evening being very fine. — With 300, the north- 

 most and farther of the 2 satellites which are in conjunction, is the smaller: I sup- 

 pose it to be the 2d. The southern and nearer of the 2 satellites in conjunction, is 

 the next in size; I suppose it to be the 1st. The 4th satellite is a little larger than 

 the larger of the 2 satellites which are in conjunction; but the difference is only 

 visible with a great deal of attention. The 3d satellite is much larger than the 4th. 



August 9, 1794, I7 h 50 ra 32 s ; 10-feet reflector; power 170; the light of the 

 1st satellite is very intense and white. The light of the 2d satellite is also pretty 

 intense and white. The light of the 3d satellite is neither so intense nor so white 

 as that of the 1st. The light of the 4th is dull and of a ruddy tinge. With 300 

 and 400, the 2d is the least, and the 3d is the largest. I am in doubt whether the 

 4th or the 1st is largest; with 600, I suppose the 1st to be larger than the 4th. 



September 30, 1795, 20 h I5 m 17 s ; 7 -feet reflector ; power 210; order of the 

 magnitudes of the satellites of Jupiter 3-2.1,4; power 110; 3-2,1 .4; with 

 460, 3-2,1,4. 



October 2, 1795, 20 h 18 m 22 s ; 7-feet reflector; power 287; Jupiter's satellites 

 3 --2 1,4. The 2d and 3d satellites are not yet in conjunction. — At 20 h 43 m 

 22 s . The conjunction between the 3d and 2d satellites is past. The distance be- 

 tween them is now one diameter of the 3d. 



August 18, 1796, 18 h 47 m 2J s ; 7-feet reflector; power 287; the 4th satellite is 



