NEWS FROM THE MOON. 233 



would not differ more than sixty-two yards from the 

 longest. This is something very different from the 

 seventy miles resulting from Grussew's measurements. 



If then that monstrous hill exists, we must look for 

 its origin in some extraneous cause, since we see that 

 a globe assuming its natural figure under such con- 

 ditions as prevailed in the moon's case would present 

 no such excrescence. I believe I am justified in 

 saying that the photographic evidence is accepted by 

 Dr. De la Eue himself. In fact, when two pictures of 

 the moon, in opposite stages of her balancing, are 

 looked at, the stereoscopic view shows Grussew's great 

 hill actually standing out, as it were, before the very 

 eyes. I venture to quote Sir John Herschel's account 

 of the principle of this method, because of the singu- 

 larly effective way in which he presents the matter. 

 He says : ' Owing to the libration of the moon, the 

 same point of her surface is seen sometimes on one 

 side of the centre of her disc, and sometimes on the 

 other, the effect being the same as if, the moon re- 

 maining fixed, the eye were shifted from right to left 

 through an angle equal to the total libration. Now 

 this is the condition on which stereoscopic vision 

 depends, so that by choosing two epochs when the 

 moon is presented in the two aspects best adapted for 

 the purpose, and taking separate and independent 

 photographs of it in each aspect, the two, stereo- 

 scopically combined, so completely satisfy all the re- 

 quisite conditions as to show the spherical form just 

 as a giant might see it, whose stature was such that the 



