THE CONSTANT FACE OF THE MOON. 55 



might then, if the season were suitable, look at Jupiter 

 again at six o'clock ; in this case the hemisphere he last 

 saw would have vanished, while that presented to him at 

 eight o'clock on the previous evening would have been 

 restored. He would again find the same belts and marks 

 as those he saw on the first occasion, altered only by such 

 intrinsic changes as may have actually taken place on the 

 planet in the interval. These illustrations will suffice to 

 indicate how different are the circumstances of the moon's 

 motion from those that we find in the other celestial bodies. 



If I were asked to offer a conjecture as to what the 

 other side of the moon may be like, I should not hesitate 

 to reply that in all probability it would present features of 

 a similar character to those on that side of our satellite 

 with which we are so familiar. The study of the sun and 

 planets shows that they are, generally speaking, symmet- 

 rical in form, and the circumstance that we happen to be 

 prevented from viewing one side of the moon does not 

 impair the analogy between it and the other orbs of heaven. 

 We should therefore expect to find on that distant side 

 of the moon indications of the same volcanic and other 

 phenomena that our telescopes show on that surface which 

 we actually see. 



We have mentioned the case of other globes which 

 revolve on their axes, the revolution being conducted in 

 such a manner that the entire surface is more or less 

 known to us. The moon also revolves on its axis, the 

 peculiarity, however, consisting in the circumstance that 

 the time taken for the rotation about its axis is equal to 

 that of its revolution round the earth. An old paradox is 

 connected with this question, for as the moon does not 



