COMPOUND MOTION. 



33 



teams attached to a plow or to a wagon very nearly 

 in a straight hne with the draught, or else a part of 

 the force will be lost; and also the importance, when 

 several animals are drawing together, of their working 

 as nearly as possible in the same straight hne. For, 

 the more such forces deviate from a right line, the 

 more they will tend to destroy or neutralize each other. 

 A famihar example of the result of two oblique forces 

 is furnished when a boat is rowed across a river. If 

 the river has no current, the boat will pass directly 

 from bank to bank perpendicularly ; but if there is a 



strilvc the opposite bank lower down, according to the 

 rapidity of the stream and the slowness of the boat. 



Another instance is afforded when a ferry-boat is 

 anchored, by means of a long rope, to a pomt some 

 distance above {Fig. 10); the boat bemg turned 



Fig. 10. 



obhquely, will pass from one bank to the other by the 

 force of the current. Here the water tends to carry 

 the boat downward, wliile the force of the rope acts 

 upward ; the boat passes between the two from bank, 

 to bank. The ascent of a kite is precisely similar, the 

 wind and the string being counteracting forces. When 

 a vessel sails under a side-wind, the resistance of the 

 keel against the water, and the force of the wind 

 against the sail, act in different directions, and pro- 

 duce a motion of the vessel between them. 

 B2 



