55 



also that all the resisting force of the air, that is the fulcrum, should be applied 

 at a point, which would be somewhere not very far from the end of the wing, for 

 the resistance of the air is necessarily much more intense near the tip of the 

 wing than near the body. 



Thus we may say for sake of clearness that the action of a wing in flight 

 is the same as the action of a rigid rod placed across a bar, which is the fulcrum, 

 and which rod has a weight at one end and a power or force at the other end, 

 both of which pull or act in the same direction. Now it is a fact in mechanics 

 that the length of the lever from the fulcrum to the power multiplied into the 

 power, must equal the length of the lever from the fulci-um to the weight 

 multiplied into the weight, to produce a balance or equipoise, and therefore 

 it is apparent that tlie shorter the arm of the lever next to the power the 

 greater must be the power in order to balance the weight. Now that is just the 

 case with a \ving, for the fulcrum there is nearer to the end of the wing, or 

 where the power is applied, than to the body of the bird or the weight, and 

 therefore, as we have seen above, it will be necessary, to produce balance, that 

 the power should exceed the weight. In flight, however, more than balance is 

 required, for it is necessary that the body or weight should be lifted, therefore 

 it is evident that a much more intense force is needed. 



From the foregoing arguments it may be concluded that the power or force 

 applied in the stroke of the wing is considerably greater than the weight of the 

 bird's body. 



We may sum up, therefore, the me<Shanical principle of the swtion of the 

 wing in flight, as that of a lever of the first kind, where power and weight are 

 acting in the same direction but on opposite sides of the fulcrum, the power being 

 applied to the shorter arm of the fulcrum, and therefore requii'ing to be con- 

 siderably greater than the weight. 



Before proceeding to notice the niceties of adjustment found in the wing, 

 and the methods in which progression, soaring, hovering, and other motions are 

 attained, I will just pause for a moment to point out that the wing, with 

 reference to the body, may be regarded as a lever of another kind. That is 

 a lever where the power and the weight are on the same side of the fulcnim 

 but act in opposite directions, and where the power is next to the fulcrum. This, 

 which is called the third kind of lever, is the class to which all bones and muscles 

 belong, for in the case of the wing the fulcrum is the shoulder joint ; the power 

 is the muscle or tendon apphed just over the joint, and the weight is either 

 the Umb itself or some actual weight attached at the other extremity. 



In this kind of lever the power must always be in excess of the weight, 

 and therefore this kind is never used in mechanical operations for raising 

 weights, but inthe animal organisation it is the kind always found, because the 

 fulcrum and the power are thus placed close together, and a great economy of 

 «pace and compactness is gained. 



