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Brightness of the Satellites of Jupiter. 
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 
brightness, not magnitude. 
The 1st is very bright. 
September 15, 179b. 19 11 25 25". 10-feet reflector; power 
300. The 2d satellite of Jupiter is a little less than the 1st. 
The 3d is much larger than any of the rest. 
Power boo. The difference in the magnitude of the 1st and 
2d satellites, with this power, is pretty considerable. 
September 2 1, 179b. i9 h 24' 5". 10-feet reflector; power boo. 
The shadow of the 1st satellite is upon one of the dark belts 
of Jupiter. 
In order to use very high powers with this telescope, I tried 
it upon the double star ^Aquarii with 1200. The air is very 
tremulous, but I see now and then the two 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 boo. 
With 400, it is nearly as bright as the brighter part of the pla^ 
net, 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. 
Yy 
MDCCXCVII. 
