THE CONSTANT FACE OF THE MOON. 53 



satellite which have been observed from all antiquity, and 

 whenever the surface of the moon can be seen, the same 

 marks are always discernible. I ought, however, to qualify 

 this remark by saying that the face of the moon is some- 

 times tilted a little, so that the objects found close to the 

 edge are not always unchanged. Speaking generally, 

 however, there is hardly a more striking fact in the celes- 

 tial movements than the constant face of our satellite. We 

 have little doubt that the moon, like the other heavenly 

 bodies, is globular in its form, but we have never been 

 actually able to see that the opposite side of the moon has 

 the hemispherical shape that we find possessed by the side 

 which is presented to us. As we have not the means of 

 holding up a looking-glass behind the moon there seems to 

 be no possibility of learning what is at the other side. 



We may perhaps emphasize the remarkable attitude of 

 the moon towards the earth, by contrasting it with that of 

 some of the other celestial bodies. Consider, for instance, 

 the corresponding circumstances with regard to the sun. 

 It is true that our great luminary exhibits to us no per- 

 manent features like those which are engraved on the 

 moon's face, but the spots on the sun, transient though 

 they doubtless are, still endure long enough to testify con 

 clusively that the sun rotates on its axis. We learn in fact 

 from a vast accumulation of observations specially directed 

 to this one point that the period of the rotation of the 

 sun is certainly more than three weeks, and certainly less 

 than four. Hence that side of the great luminary which 

 is directed towards the earth must be constantly changing. 

 If we look on one hemisphere of the sun to-day, then a 

 fortnight ago it was the opposite hemisphere that was 



