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of them look dark) when crossing Jupiter’s disc, so that we have 
to deal with a circumstance peculiar to the fourth or outermost 
satellite. Nevertheless, we seem precluded from supposing that 
any other difference exists between this satellite and the others 
than a certain inferiority of light-reflecting power. I might 
indeed find an argument for the view which I have suggested as 
not improbable, that Jupiter is a heat-sun to his satellites, since 
the three innermost would be in that case much better warmed 
than the outermost, and therefore would be much more likely 
to be cloud-encompassed, and so would reflect more light. But I 
place no great reliance on reasoning so ingenious, which stands 
much as a pyramid would stand (theoretically) on its apex. 
The broad fact that a body like the fourth satellite, probably 
comparable to our moon in light-reflecting power, looks per- 
fectly black when on the middle of Jupiter’s disc, is that on 
which I place reliance. This manifestly indicates a remarkable 
difference between the brightness of Jupiter and the satellite; 
and it is clear that the excess of Jupiter’s brightness is in accor- 
dance with the theory that he shiues in part with native light, 
or, in other words, is intensely heated. 
This completes the statement of the evidence obtained 
during the recent opposition of Jupiter in favour of a theory 
which already had the great advantage of according with all 
known facts, and accounting for some which had hitherto 
seemed inexplicable. If this theory removes Jupiter from the 
position assigned to him by Brewster as the noblest of inhabited 
worlds, it indicates for him a higher position as a subordinate 
sun, nourishing with his heat, as he sways by his attractive 
energy, the scheme of worlds which circles round him. The 
theory removes also the difficulty suggested by the apparent 
uselessness of the Jovian satellites in the scheme of creation. 
When, instead of considering their small power of supplying 
Jupiter with light, we consider the power which, owing to his 
great size and proximity, he must possess of illuminating them 
with reflected light, and warming them with his native heat, 
we find a harmony and beauty in the Jovian system which 
before had been wanting ; nor, when we consider the office which 
the Sun subserves towards the members of his family, need we 
reject this view on account of the supposition — 
That bodies bright and greater should not serve 
The less not bright. 
