BIRDS AS FLYING MACHINES. 473 



BIRDS AS FLYING MACHINES. 



By FREDERICK A LUCAS. 



FROM the day of Solomon onward the way of a hird in the air has 

 been a subject of general interest, and the attention given to the 

 problem of aerial navigation of late years has caused the flight of birds 

 to be carefully studied in the hope that it might throw some light on 

 the subject. There have been many conceptions, not to say misconcep- 

 tions, regarding the flight of birds; it has been assumed that their 

 muscles exerted a power quite beyond that of other animals, that the 

 air sacs of some birds and the hollow bones of others gave them a de- 

 gree of lightness quite unattainable by the use of ordinary materials, 

 while some have even gone so far as to suggest the presence of some 

 mysterious power, something like Stockton's negative gravity, whereby 

 birds could set at naught the law of gravitation and rise at will like a 

 balloon. The strength of a bird's muscles, of some birds' muscles at 

 least, is not to be underrated; a hawk will plant its talons in a bird of 

 nearly its own size and weight and bear the victim bodily away, and an 

 osprey will carry a fish for a long distance. But a tiger has been known 

 to fell a bullock with a single blow of the paw, to carry a man as a cat 

 would carry a rat and to drag an Indian buffalo heavier than himself. 

 On the other hand, some of the petrels, birds which can pass a day or 

 so on the wing with ease, cannot rise from the water after a hearty meal, 

 and the humming-bird, unsurpassed in aerial evolutions, may be trapped 

 in a spider's web. This shows no great power, and long ago Marey 

 found that the pulling force of a hawk's great breast muscle, applied 

 through the humerus, amounted to 1,298 grams per square centimeter, 

 something like seven pounds to the square inch; not a very heavy pull. 

 So it seems fair to assume that while the power exerted by a bird is 

 great, it is very far from marvelous, probably far less in proportion to 

 size than the engine of Maxim's great aeroplane, or the naphtha motor 

 of Professor Langley, which weighs less than ten pounds per horse 

 power. We may get a fair idea of what this means by remembering 

 that a bald eagle weighs from nine to fifteen pounds and that he exerts 

 but a small fraction of a horse power. 



Turning to the question of the part played by the air sacs it may be 

 said that their value is not proved; some of the fastest birds get along 

 without them, while birds of the most labored flight are sometimes well 

 provided. In birds like the gannet and brown pelican the air sacs and 

 cellular tissue about the body undoubtedly serve as buffers to break the 



