442 THE POPULAR SCIENCE MONTHLY. 



not imagine that such an intensely black object would be visible when 

 off the disk, and waited with some impatience to see the emersion, but 

 were disappointed by fog, which came on just at the critical time." 

 Another observer, using a telescope only two inches in aperture, saw 

 the satellite when off the disk, so that manifestly the blackness was 

 merely an effect of contrast. 



In considering this remarkable phenomenon, we must not forget 

 that the other satellites do not look black (though some of them look 

 dark) when crossing Jupiter's disk, so that we have to deal with a 

 circumstance peculiar to the fourth or outermost satellite. Neverthe- 

 less, we seem precluded from supposing that any other difference ex- 

 ists 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 perfectly black when on the middle of 

 Jupiter's disk, is that on which I place reliance. This manifestly in- 

 dicates a remarkable difference between the brightness of Jupiter and 

 the satellite ; and it is clear that the excess of Jupiter's brightness is 

 in accordance with the theory that he shines 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 favor of a theory which already had 

 the great advantage of according with all known facts, and account- 

 ing 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 attrac- 

 tive 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 consid- 

 ering £heir small power of supplying Jupiter with light, we consider 

 the power which, owing to his great size and proximity, he must pos- 

 sess 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 w T e consider the 

 office which the sun subserves toward the members of his family, need 

 we reject this view on account of the supposition — 



M That bodies bright and greater should not serve 

 The l$ss not bright." 



— Popular Science Review. 



