THE EARTH 135 



once mingled in a nebula, and were evolved 

 according to some one of the nebular hypotheses 

 we have already described. The principal 

 members of the solar system are Mercury, Mars, 

 the Earth, Venus, Jupiter, Saturn, Uranus, and 

 Neptune. The innermost planet is Mercury and 

 the outermost Neptune, and the others come in 

 succession in the order in which we have named 

 them, the Earth accordingly spinning round the 

 Sun between Mars and Venus. 



The Earth is about 8000 miles in diameter : it 

 is larger than Mercury and Mars, and about the 

 same size as Venus ; but compared with the outer 

 four planets it is only a pigmy, and compared 

 with the Sun it is a midge to a football. Jupiter 

 is more than a thousand times, and the Sun more 

 than a million times the size of the Earth ; and 

 we may mention, en passant^ that there are many 

 stars in space much larger than our Sun. The 

 Earth cannot, therefore, claim to be very big, and 

 is hardly big enough to be the hub of the universe. 

 But it has a good deal of pace ; it not only spins 

 on its axis, but it yearly runs 583,000,000 miles 

 round the Sun, at the rate of eighteen miles a 

 second — that is to say it moves almost a hundred 

 times as fast as a bullet from a rifle, and more 

 than a thousand times as fast as an express train. 

 That is certainly a good pace, yet Mercury and 



