vii FLIGHT 179 



each, for their fixed point. The fact is that the dis- 

 tinction between the fulcrum and the weight is an 

 artificial one. The power applied acts on both ends 

 at once, and if only one moves, or if one moves more 

 than the other, we speak of the weight as being at 

 that end. A weight at the other end which does not 

 give, or gives less, we call the fulcrum. In a bird's 

 wing both ends move, but since the object is to obtain 

 for the extremity as fixed a point as possible and to 

 raise the body, the term fulcrum is reserved for the 

 air. The bald statement, " The air is the fulcrum," is not 

 incorrect, but it leaves out of sight a most interesting 

 process. It is the rapid motion of the wing that wins 

 for it a comparatively fixed point, and throughout the 

 process the air is being moved by a lever that has for 

 its fulcrum the shoulder-joint. The oar, though a lever 

 of the second order, presents the same difficulty, but in 

 a less puzzling form. People who have never thought 

 of the subject are apt if asked what is the fulcrum on 

 which an oar works, to reply " the rowlock." This is 

 as much as to say that it is the aim of the oarsman 

 to displace as much water as possible. It is only, 

 however, by making the displacement of water a 

 preliminary object, that he gains a fulcrum by which 

 to move his boat. 



We must now consider the working of both wings 

 at once. In order to understand this we may imagine 

 a boat rowed by oars employed as levers of the same 

 order as a bird's wings. The rowlocks would be in 

 the middle of the boat, and the oarsman would sit on 

 either side holding the oars between rowlock and 

 blade. They would have to face the bows, and this, 



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