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Introduction to the Study of Science 



where large timber was scarce or unknown, rafts were made of 

 small logs, such as bamboo stalks, tied together ; or boats were 

 made of tough bark or skins fastened over a frame (Fig. 114). 

 Such were the birchbark canoes of American Indians, the skin 



canoes or kyacks of the 

 Eskimos, and the round 

 skin boats used on the 

 Euphrates River. 



When in later ages men 

 began to build boats of 

 hewn planks, they opened 

 the way for new achieve- 

 ments not only in the con- 

 struction, but also in the 

 propelling of boats. With 

 the discovery of the sail as 

 a means of making use of 

 wind as a motive power, a 

 new era of water travel and 

 transportation was begun. 



Youth to-day frequently 

 begins its experience in water 

 navigation with craft similar to those used by men in primitive 

 times. The rude raft or float, the flat-bottomed boat, the row- 

 boat, and the canoe, and eventually the motor boat follow in 

 the experience of youth in somewhat the same order as they 

 did in the course of human history. The motor boat and the 

 sailboat usually come late in the series. 



I. BUOYANCY 



149. Why a boat floats. In all kinds of floating and sailing 

 craft there is one problem to which attention is required. We 

 are generally familiar with the various kinds of motive power 

 employed, but we may not always understand why a boat or 

 any other object floats. A boy weighing seventy-five pounds 



FIG. 114. Primitive circular boats and 

 modern steamships on the Tigris River. 

 (From London Illustrated News.) 



