92 THE BORDERLAND OF SCIENCE. 



The bright belts according to this view, are regarded 

 as zones where for the time clouds are prevalent, the 

 dark belts being regions where the comparatively dark 

 hues of the planet's surface are brought into view. 

 And then it has been deemed sufficient to point out 

 that the parallelism of the zones is due to the extreme 

 rapidity of the planet's rotation. 



But setting aside the fact that the trade-wind zones 

 and the great equatorial calm zone on our earth are, in 

 reality, little better than meteorological myths, it must 

 be regarded as a remarkable fact that, in the case of a 

 planet so far away from the sun as Jupiter is, there 

 should be a supply of clouds so abundant as to form 

 belts discernible from the earth. Jupiter is rather 

 more than five times farther from the sun than the 

 earth is, and receives from him about one twenty- 

 seventh part of the light and heat which falls upon the 

 earth (equal surface for equal surface). Making every 

 allowance for the possibility pointed out by Professor 

 Tyndall, that some quality in Jupiter's atmosphere 

 may prevent the solar heat from escaping, and so 

 cause the climate of the planet to be not very different 

 from the earth's, yet the direct heat falling on the 

 planet's oceans cannot be increased in this way nay, 

 it must be rather diminished. It chances, indeed, 

 that the very quality by which the earth's atmosphere 

 retains the solar heat is unquestionably possessed by 

 Jupiter's atmosphere. When our air is full of aqueous 

 vapour (invisible to the eye) the escape of heat is 

 prevented, as Tyndall has shown, and thus the nights 



