How Canal-boats are Lowered. 



Boat descending: and about to enter the lock. 



15. When a boat is to go from a high to a 

 low level, the order of opening and closing 

 the gates is simply reversed. 



1 6. When the boat reaches the upper, closed gates, the 

 lower gates are closed ; then the water is let into the lock 

 until it is full. The upper gates are then swung open 

 against the sides of the canal and the boat enters the lock. 





Boat in lock, and about to descend to the lower level. 



17. It is now easy to see that by letting the water 

 out of the lock and by opening the lower gates, the upper 

 gates remaining closed, the boat settles down with the 

 water and passes out on the lower level. 



