188 PHILOSOPHICAL TRANSACTIONS. [ANNO 1797. 



gained by throwing open, to other observers, the road it will be eligible to take for a 

 satisfactory investigation of the subject , especially as we have reason to congratulate 

 ourselves on the spirit of observation, and increase of large instruments, that seem 

 to have taken place in various parts of Europe. The observations from my jour- 

 nals are as follow. 



OBSERVATIONS. 



j4 remarkable conjunction of two satellites of Jupiter. — May 14, 1790, 1 l h 30 m 

 10 s , correct sidereal time. The 2d and 3d satellites of Jupiter are so closely in 

 conjunction, that with a 7-feet reflector, charged with a magnifying power of 350, 

 I cannot see a division between them. At 1 l h 34 m 10 s , the shadow of the 1st sa- 

 tellite is still on the disc of the planet. 



Intenseness of light and colour of the satellites. — July 19, 1794, 1 7 h 12 m 47 s , 

 7-feet reflector: the 1st satellite of Jupiter is of a very intense bright, white, shin- 

 ing light. It is brighter than the 2d or 4th. I speak only of the light, and not 

 of the size. — The colour of the 4th satellite is inclining to red. In brightness it 

 is very nearly, but not quite equal to the 2d. — 10-feet reflector, power 170 : the 3d 

 satellite is just gone upon the body; before it went on^ it appeared to be smaller' 

 than usual. — The 2d satellite is of a dull, ash-colour ; not in the extreme, but ra- 

 ther inclining to that tint. — July 21, 1794, l6 h 56 m 45 s ; 10-feet reflector; power 

 170 : the 3d satellite of Jupiter is round, large, and well defined. It is very bright, 

 and its light is very white. — The 4th satellite is also round, large, and well defined. 

 I estimate its magnitude in proportion to that of the 3d satellite to be as 4 to 5. 

 Its light is not white, but inclined to orange. 



Brightness and diameter distinguished. — July 26, 1794, I7 h 14 m 41 s ; 10-feet 

 reflector; power 170 : The 4th satellite is very dim : it is of a pale, dusky, reddish 

 colour. The 2d satellite is of a bright, white colour. The 3d satellite is very 

 bright, and white. The 1st satellite is very brilliant, and white. At 17 h 22 ra 41 s , 

 the magnitudes with 240, were thus : the 3d satellite is the largest : the 2d satel- 

 lite is the smallest. With 300, the 4th satellite is a very little larger than the 2d, 

 though less bright. The 1st satellite is larger than either the 4th or 2d. With 

 400, the order of the magnitudes is 3 1 4 2. With the same power, the order of 

 the light is 3 1 2 4. 



Diameter of the second satellite by entering on the disc of the planet. — 

 July 28, 1794, I7 h 25 m 40 s ; 10-feet reflector; power 170: the 2d satellite is 

 nearly in contact with the following limb of Jupiter. — I7 h 29 m 40 s , it seems to be 

 very near the contact : with 300, very near the contact. — I7 h 30 m 40 s , it seems to 

 be in contact: it is brighter than that part of Jupiter where it enters. — I7 h 31 m 

 40 s , it is more than half entered. — I7 h 33 m 40', it seems to be nearly quite en- 

 tered: its superior brightness makes it seem protuberant. — I7 h 34 m 40 s , it is cer- 

 tainly quite entered. — 17 h 35 m 25 s , I see a little of the disc of Jupiter on the out- 

 side of the satellite, equal to about \ of its diameter. — 17 h 39 m 40 s , the 3d satellite 

 is very bright, and of its usual colour. — The 4th satellite is faint, and also of its 



