Canal-locks How Constructed. 81 



voyage from Lake Superior or Lake Michigan includes 

 Lake Huron and Lake Erie. 



5. The only difficulty about some canals is 

 that they will freeze up in winter. Then the 

 railroads get the better of them, and carry large 

 quantities of goods during the long winter 

 months. 



6. This large canal, however, which is called 

 the Erie Canal, is only about half as long as 

 one in China, which runs from the great city 

 of Pekin to the great river Yangtse Kiang. 

 There are said to be about four hundred canals 

 in China. 



7. These are used not only as water highways to float 

 goods or produce from place to place, but also for irriga- 

 tion that is, to water the fields, so that the plants may 

 grow better, and thus yield a more abundant crop. 



8. In Egypt, where it very seldom rains, the land is 

 watered in this way by water from the Nile River. 



9. In canals they have a curious way of mak- 

 ing boats climb up hill ; for canals must some- 

 times be made on ground that is high in one 

 part and low in another. Where a high and a 

 low level meet, as shown in the blackboard 

 drawing, it is necessary to build what is called a 

 lock, perhaps because it locks the parts together. 

 This is a shaft or well-hole of stone, carefully 

 laid in cement so as to be water-tight, ex- 

 tending down from the upper to the lower level 



