VENUS AND MERCURY. 143 



crescent of light, the irregularities near the horns of the 

 crescent could be attributed to mountains on the surface ; 

 while some astronomers had the hardihood to attempt to 

 calculate the elevation of the mountains which would give 

 rise to the features that were noticed. It can hardly be 

 said at any time that these observations and inferences com- 

 manded any very large degree of credence among those 

 competent to judge. From the facts which have recently 

 come to light, and which form the subject of this sketch, it 

 seems certain that even the small amount of belief which 

 was accorded to these researches must now be almost 

 entirely withheld. 



There are many reasons why it should be of special 

 interest to learn all that we can of the topography of this 

 planet, which lies so near us. It so happens that Venus 

 has a bulk which is very nearly the same as that of the 

 earth. It seems also to be quite certain that Venus is 

 clothed with an atmosphere, for it would be otherwise im- 

 possible to explain the girdle of light which surrounds 

 the planet when she is in front of the sun's disc. The 

 measures of heat and light from the great luminary which 

 are received by Venus are, no doubt, in excess of those 

 which fall to the earth's share ; but still it seems that Venus 

 is a world so like our own in many respects that every 

 element of intellectual curiosity excites us to learn all 

 we can about another world to which we are linked by so 

 many affinities. There seems no prospect that we shall 

 ever perceive the features of the planet as fully and aa 

 minutely as we shall learn those of Mars. However, one 

 step has now been taken, and the results are pregnant with 

 interest. 



