19° PHILOSOPHICAL TRANSACTIONS. [ANNO 1797. 



less bright than the 1st; though the latter is so near the planet as to have its light 

 overpowered by Jupiter, while the 4th is at a great distance; I mean light or bright- 

 ness, not magnitude. The 1st is very bright. 



September 15, 1 796, 19 h 25 ra 25'; 10-feet reflector; power 300; the 2d satel- 

 lite of Jupiter is a little less than the 1st. The 3d is much larger than any of the 

 rest. — With the power 600 the difference in the magnitude of the 1st and 2d sa- 

 tellites, with this power, is pretty considerable. 



September 21, 179^» 19 h 24 m 5*; 10-feet reflector; power 600; the shadow of 

 the 1st satellite is on one of the dark belts of Jupiter. In order to use very high 

 powers with this telescope, I tried it on the double star f Aquarii with 1200. The 

 air is very tremulous, but I see now and then the 2 stars of this double star very 

 well defined. With the same power, the satellites of Jupiter are very large, but 

 not so well defined as the above star. 



The brightness of the satellites compared to the belts and disc of the planet. — The 

 1st satellite, which is lately come off the southern belt, is nearly of the same 

 brightness with that belt; power 600. With 400, it is nearly as bright as the 

 brighter part of the planet, or rather a mean between the belt and the planet. 

 The 2d satellite is considerably bright ; its colour is whiter than that of the 1st; it 

 is however not so white as the colour of the bright part of Jupiter. The colour of 

 the 4th satellite is as dingy as that of the belt; very much less bright and less 

 white than that of the 2d. The brightness of the 3d satellite is not intense; its 

 colour however is white, though not so white as the bright part of the planet. 



September 24, 1796, 20 h 55 m 24 s ; 10-feet reflector; power 000; the 1st sa- 

 tellite of Jupiter is very bright, and of a white colour; it is also very large. The 

 2d satellite is faint and bluish; its light is not much brighter than that of the belt. 

 The 3d satellite is pretty bright; its light is whitish; it seems to be comparatively 

 less than it ought to be; or rather, its apparent smallness is owing to the uncommon 

 largeness of the 1st. The 1st satellite, with 200, compared to the 3d, is propor- 

 tionally larger than I have seen it before. 



September 30, 1796, 20 h 8 m 4 s ; 10-feet reflector; power 000; the satellites of 

 Jupiter are well defined, and the night is beautiful. The 3d satellite, in proportion 

 to the 1st, is much larger than it was September 24; I ascribe the change to an 

 apparent diminution of the 1st. — At 20 h 30 m 4 s , the 1st satellite is evidently less in 

 proportion to the 3d, than it was September 24. The 2d satellite is considerably 

 bright; its light is whitish; much brighter than the belt, but not so bright as the 

 bright part of the disc; its magnitude is less than that of the 4th; but its light is 

 considerably superior. The 3d satellite is remarkably well defined; its light is con- 

 siderably brighter than that of the belts. The magnitude of the 1st satellite exceeds 

 that of the 2d; it is nearly equal to that of the 4th. — At 22 h 58 m 4 s , appearances 

 as before. 



October 15, 1796, 2l h 23 m 42 s ; 10 feet reflector; power 600; the 2d satellite 

 is uncommonly bright; its apparent magnitude is also larger than usual. The 4th 



