592 SUPPLEMENT. 



With a good glass and careful concealment in the lantern-top, a very 

 near view was obtained. Humboldt and Darwin — the latter in The 

 Voyage of the Beagle — have given some attention to the subject, but 

 express an inability to comprehend it. The fact that these birds 

 soar, or remain apparently motionless, only when the wind is con- 

 siderable, seems to have escaped their notice. For therein lies the 

 secret. The Tachypetes represents the most spread of wing and the 

 least proportionate body of any bird, and is, consequently, one that 

 possesses the greatest faculty for maintaining the curious position 

 in mid-air. Another fact is, the bird always faces the wind. We 

 have, then, the same conditions as in the case of a boy's kite. It 

 rises precisely as a kite does, and it moves only as it does — not by 

 any movement of feathers, but a gentle swaying, and a trifle of tilt- 

 ing on the wing, to maintain its balance. What keeps it from being 

 blown away — for the kite has its string ? The intelligence of the bird 

 causes it to tilt fonvard just enough to counteract the force of the 

 wind, and thus the smallest space is presented to the wind ; it is 

 merely a thin edge. Tijjping forward causes the body to fall against 

 the wind ; the two forces — gravity and the wind — are opposed, and 

 a perfect rest is the rer.ult. 



The writer received a note from Mr. Darwin, in answer to one sug- 

 gesting this explanation. In this answer he says : "I have thought 

 of some such explanation, but the mathematicians say it is not pos- 

 ble ; that the two forces do not operate in a direct line, opposite to 

 each other." Now, there is the qualifying iDOwer of buoyancy, which 

 operates to prevent the bird from dropping directly down like a 

 dead weight. We must regard the bird as it is — a thin, exceed- 

 ingly light object, that is kept \vji by a strong wind, and that, by its 

 intelligent attention, keeps the outspread wings and body rigid and 

 always edge-wise to the wind, with a slight tendency downward. 

 These conditions observed, the bird i^ests upon the wind as the kite 

 does, the force of gravity operating as the string. It is not uncom- 

 mon to see a stiff piece of paper balanced in the air by the wind, and 

 when inclined even directly against the wind, to shoot forward 

 until it goes obliquely to the ground. Now, could this jDaper, just 

 at the moment of falling, while inclined against the wind, act to tilt 

 its face a trifle, the wind would send it backward and upward 

 again. Thus, if the two forces were opposed by intelligent action, 

 the result would be as in the bird, a complete balancing on the wind. 



AiiCA iMPENNis. Great Auk. — This bird is notable in the sense 

 that it has ceased to exist, so far as its history is cognizant, and is 



