THE EMPIRE OF THE AIR. 419 



barely sustain it. Yet, actually measured ami weighed, it pieseuts 

 the following' surx)nsiug- results: 



It weighs only 0.92 pound per square foot of sustaining surface, 

 body and wings, aud this is less than the flamingo, which weighs 1.56 

 pounds per square foot of surface, and yet this rosy wader is generally 

 thought of as a mere i^ack of feathers. Or than the pelican, which 

 weighs 1.3G j)Ounds i)er square foot, and which flies very well- Or than 

 the stormy petrel, which weighs 1.17 pounds i)er square foot, and must 

 depend upon speed for a living. Or, it wdl not be believed, the quail 

 weighs actually less than the tawny vulture, which weighs 1.47 pounds 

 to the scpiare foot of surface, and yet floats for whole days without a 

 single flap. And yet how badly the poor quail flies! Its usual course 

 is 200 yards, and it is then outflown, it pants for breath. 



I'rom the comi>arison of the rates existing between the weights and 

 the surfaces of the birds which I have jueasured and inscribed in the 

 tables of this work, \ may deduce a general law: The amount of ])ro- 

 portionate surface re([uircd l)y a bird for a given mode of flight dimin- 

 ishes as the weight of the bird increases. 



The exact proportion is yet to be deduced from more complete tables 

 than those which I i)resent. and from experiments to be made upon 

 the sustaining power of aeroplanes constructed upcm siiniliar models, 

 but of difierent sizes, and loaded Avith ballast until they produce similar 

 satisfactory results. 



The exact advantage obtained through large mass, while indicated 

 by my tables in a decided and regular manner, is somewhat difticult to 

 formulate. The manner of increase of the volume, in relation to the 

 containing i»erij)hery, certainly cuts a figure; it is a factor to the credit 

 of the larger mass, by diminishing the relative air resistance; this is 

 un(piesti(mable. Increasing sustaining surfaces, on flie other hand, 

 l)roduces increased friction and resistance, but the gains and U)sses do 

 not iiHirease with the same factors, and hence result complications. 



We might reasonably expect that the area of surface required to 

 sustain each pound of l)ir<l would be a. fixed and definite ratio; any 

 <leviation should only be prodnced through gain in the ratio Ix^tween 

 the volume and its enveloping surface, or through loss by increased 

 resistance and friction of the sustaining surfaces. And yet it is not so. 

 The tables I have constructed show that things are a ery difierent : they 

 indicate enormous discrepancies. 



Thus the surface of 3.<)2 square feet required to sustain one pound of 

 bank-swallow is reduced in the tawny vulture (whicli flies and is sns 

 tained at least as well), to O.OS square feet per ])Ound, a variation of 

 five times and more. 



If we seek an exjdanation for this ])henomenon, we find that a dis- 

 turbing <'ause always ])rings advantage to the larger mass; it is the 

 variation in the coefli<'ientof air resistances opposed to difierent masses. 

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