COMMON THINGS 23 



that the mud is quite soft under a railway-bridge. Ex- 

 plain these differences. 



10. Why is the breast-meat of a fowl white, and the 

 Irtf-meat dark ? Mention birds which come to table 

 whose breast-meat is dark. 



11. Why does a pan of milk boil over sooner than a 

 pan of water ? 



12. In how many different ways can you tell the north ? 



13. Of what advantage is it to a horse-chestnut that its 

 young leaves droop, and hang vertically ? 



14. Design two wheelbarrows, one suitable for wheeling 

 garden rubbish, the other suitable for wheeling lumps of 

 iron or lead. 



15. Why do we slide the hand toward the coal when 

 lifting a heavy lump with a pair of tongs ? 



16. Why do we swing the hands to and fro, when walk- 

 ing fast ? 



I will add a question which I cannot answer fully, 



I hough I have puzzled over it for years. Why do the 

 leaves of the aspen and some other poplars quiver ? It 

 is easy to see how they do it ; a glance at the leaf-stalk 

 is enough. But what is the advantage of the quivering 

 leaves ? (See p. 195.) 



Many years ago Charles Waterton set the fashion of 

 puzzling his readers with hard questions. Why, he asks, 

 has one cow horns and another none ? Why does a dog 

 lap water, and a sheep drink it ? Why has a horse large 

 warts on the inside of his legs ? Why does cock-robin 

 sing for twelve months consecutively, whilst his com- 

 panion, the chaffinch, warbles but half the time ? l 



" A boy or girl," says Herbert Spencer, " rising in the 

 teens, might with advantage be asked How happens it 

 that in hilly counties such as Devonshire, the lanes are 

 <l-p down below the surface of the adjacent fields; 

 win Teas in flat counties the surfaces of the lanes and of 



II ic fields are on the same level ? What is the definite 



1 Essays on Natural History. 



