BIRDS AS FLYING MACHINES. 475 



every intermediate stage between the two, or combinations of flapping 

 and sailing, and as a matter of fact no bird can entirely dispense with 

 strokes of the wing. 



The humming-bird represents the perfection of one method, the 

 frigate bird of the other, and in his own line each is unrivaled. These 

 two modes of flight are associated with equally distinct modifications 

 of structure, and just as we have every intermediate state of flight be- 

 tween flapping and soaring so the two structural extremes are merged 

 into one another. The humming-bird flies as the Irishman played the 

 fiddle, by main strength, the frigate bird relies on his skill in taking 

 advantage of every varying current of air, and the skeleton of the one 

 indicates great muscular power while that of the other shows its ab- 

 sence. No other bird has such proportionately great muscles as the 

 humming-bird, the keel of the sternum or breast bone from which these 

 muscles arise runs from one end of the body to the other while at the 

 same time it projects downward like the keel of a modern racing yacht. 

 These muscles drive at the rate of several hundred strokes a minute a 

 pair of small, rigid wings, the outermost bones of which are very long 

 while the innermost are very short, a feature calculated to give the 

 greatest amount of motion at the tip of the wing witli the least move- 

 ment of the bones of the upper arm, to which the driving muscles are 

 attached. Another peculiar feature is that the outermost feathers, the 

 flight feathers or primaries, are long and strong, while the innermost, 

 those attached to the forearm, are few and weak; so far as flight is con- 

 cerned the bird could dispense with these secondaries and not feel their 

 loss. Finally the heart, which we may look upon as the boiler that 

 supplies steam for this machinery, is large and powerful, as is necessary 

 for such a high-pressure engine as the little humming-bird. It is 

 hardly to him that we would look for aid in constructing a flying ma- 

 chine, the expenditure of force is too great for the results attained, 

 the space required for boiler and engine leaves no room for carrying 

 freight. 



As just intimated the frigate bird is exactly the reverse of his tiny 

 relative; the body is a mere appendage to a pair of wings, while the 

 breast muscles are so small as to show at a glance that of all flying crea- 

 tures the frigate bird is the one which has most successfully solved the 

 problem of the conservation of energy and can obtain the greatest 

 amount of power with the least expenditure of muscle. 



There is also a great difference between the hummer and the frigate 

 bird, or between flapping and sailing birds generally, in the complexity 

 of what may be termed the muscles of adjustment, the little muscles 

 that run from the shoulder to the elbow and forearm and, among other 

 duties, are concerned in keeping free from wrinkles that portion of the 

 wing which lies between the shoulder and the wrist, forming a triangu- 



