X INTRODUCTION. 



search of coals or metals have opened deep holes 

 in the ground. We might go down into one of these 

 mines, in the hope of finding out something concern- 

 ing the inside of the world ; but we should find it so 

 uncommonly dark that not a thing could be seen. 

 We may carry a lamp ; but its feeble light only shows 

 rough rocks or glistening coal, looking precisely like 

 the rocks and coals we have seen on the hillsides. 

 We stand still a while in the gloom of the mine, and 

 listen, in the hope we may hear some sound from the 

 interior of the earth that may tell us what is going 

 on there : there is nothing, nothing save intense 

 blackness, awesome stillness, deep, profound, and ter- 

 rifying. We may be glad to escape up the elevator to 

 the sunshine, well content to spend our lives upon the 

 solid ground. A trip in a balloon is quite as unsatis- 

 factory. The sky seems just as high ; the stars, the 

 sun, and the moon are no nearer; and, if we look 

 down, we find the ground extends in every direction 

 till it is lost in the distance, blue, indistinct, im- 

 mense. The air is thin and cold, and we may be 

 glad when the balloon voyage is safely over, and we 

 are once more on the good, old-fashioned ground. 



So, it appears, we have to spend our whole lives 

 upon one of the planets ; and as we cannot get inside 

 of it, and cannot get away from it, we are really pris- 

 oners on the outside or surface of the great star called 

 Earth. The air is cold and thin, the caves and mines 

 are dismal and dangerous. We do not care to stay 

 either above or below the ground ; and, though we are 



