104 THE BORDERLAND OF SCIENCE. 



This unwillingness to accept startling ideas is not to 

 be altogether reprehended, since it prevents the mind 

 from forming rash and baseless speculations. Yet we 

 must not suffer this mental habitude, excellent though 

 it may be in its proper place, to interfere with the 

 admission of conclusions which seem based on trust- 

 worthy evidence. Let us then inquire whether the 

 startling hypothesis to which we have been led by the 

 study of observed facts may not be found to be in 

 agreement with other facts not yet considered. 



It will be obvious that if the real globe of Jupiter 

 is thus intensely heated, a portion of the planet's light 

 must be inherent. Therefore we might expect that the 

 planet would shine somewhat more brightly than a globe 

 of equal size and similarly placed, shining merely by 

 reflecting the sun's light. Now two series of good ob- 

 servations have been made upon the luminosity of 

 Jupiter. One was made by the late Professor Bond, of 

 America, the other by Dr. Zollner, of Germany. Accord- 

 ing to the former, Jupiter shines more brightly than 

 he would if he reflected the whole of the light 

 falling upon him ! According to the latter, and more 

 trustworthy series, Jupiter does not indeed shine quite 

 so brightly as Professor Bond supposed, but the planet 

 yet shines three times as brightly as a globe of equal 

 size would shine, if similarly placed, but constituted 

 like Mars, and four times as brightly as such a globe 

 would shine if constituted like our moon. Jupiter 

 shines in fact very nearly as brightly as though he were 

 constituted like one of our terrestrial clouds ! 



