THE STEAMBOAT 



297 



bottle again with water and put it in the dish. What happens? 

 Why? 



Some of the latest submarines are several hundred feet 

 long. They can travel when submerged n knots an hour, 

 and on the surface 17 knots; they are able to travel 140 

 miles under water and 5000 miles on the surface. One type 

 is 21 feet wide, has accommodations for 27 men, and carries 

 provisions to last 30 days. During the European War 

 great improvements in submarines were made by the Ger- 



FiG. 1 1 8. Submarine diving. 



mans, but the exact details of construction are not yet 

 generally known. 



How the submarine is propelled. Two sources of power 

 are used for propelling the boat. When the boat is on the 

 surface, a gasoline or oil engine is used to run the boat, and 

 this also runs a dynamo which charges a storage battery. 

 When the boat is under water, the gasoline engine is shut off, 

 and the propeller is turned by a motor run by electricity 

 from the storage battery. This also furnishes electricity 

 for lighting the boat and for cooking. 



