214 



COMPOSITION AND RESOLUTION OF FORCE. 



nearly opposed to the course of a vessel may. nevertheless, be made to impel 

 it by the effect of sails. The angle B D V, formed by the sail and the direc- 

 tion of the keel, may be very oblique, as may also be the angle C D B, formed 

 by the direction of the wind and that of the sail. Therefore the angle C D V, 

 made up of these two, and which is that formed by the direction of the wind 

 and that of the keel, may be very oblique. In fig. 9, the wind is nearly contrary 



Fig. 9. 



/C 



s 



to the direction of the keel, and yet there is an impelling force expressed 

 by the line D H, the line C D expressing, as before, the whole force of the 

 wind. 



In this example there are two successive decompositions of force. First, 

 the original force of the wind C D is resolved into two, E D and F D ; and 

 next the element E D, or its equal D G, is resolved into D I and D H ; so 



that the original force is resolved into three, viz., F D, D I, D H, which, taken 

 together, are mechanically equivalent to it. The part F D is entirely ineffect- 



