242 NA.TUBAL HISTORY SOCIETY OF DUBLIN. 



quite rigid the whole time. To such an extent does he do this, that iu 

 sweeping round, his wings are often pointed in a direction nearly per- 

 pendicular to the sea; and this position of the wings, more or less in- 

 clined to the horizon, is seen always and only when the bird is turn- 

 ing. It will be observed that on this principle an Albatross sail- 

 ing down wind must necessarily be descending, unless his pace is 

 much greater than that of the air, and such I have found to be inva- 

 riably the case. It may be objected that the resistance of the air must 

 soon destroy his momentum ; but the fact is, that it does not do so. A 

 good illustration of this is seen in an experiment, common in lecture 

 rooms a few years ago, by which the rotation of the earth was demon- 

 strated by means of a pendulum, composed of a metal ball suspended 

 by a string from the ceiling of the lecture hall. The impetus obtained 

 by causing the metal ball to fall through the space of a few feet only 

 was sufficient to keep the pendulum swinging with a velocity but 

 little diminished for the greater part of an hour, notwithstanding the re- 

 sistance of the sand, which the point of the pendulum had to cut 

 through twice during each vibration. The resistance of the air is well 

 known to depend on the shape and velocity of the moving body, and to 

 increase in proportion much more rapidly than the velocity increases. 

 Por this reason, a properly shaped body and a low velocity are required 

 to reduce it to a minimum. A certain amount of weight is also neces- 

 sary to give a bird momentum sufficient to overcume the resistance 

 for a certain time, and wings are required of sufficient expanse to sup- 

 port it as it sails slowly through the air. These conditions are admi- 

 rably carried out in the Albatross ; its expanse of wing is perhaps 

 greater than that of any other bird, and its weight, 15lbs. and upwards, 

 is very large. Its shape, also, when the neck is stretched out, as in 

 flying, approaches very nearly to that of Newton's solid of least resist- 

 ance, while more than one voyager has remarked the slowness with 

 which it sails past. The Petrels now under consideration sail very 

 nearly in proportion to their size and weight. The Stormy Petrel never 

 sails ; the Cape Pigeon, only for a very short time, perhaps a minute ; 

 the Night Hawk, much longer, often between five and six minutes ; 

 while the Albatross, as I have before mentioned, sometimes for an hour, 

 " rising and falling," says Dr. Bennett, "as if some concealed power 

 guided its various motions without any muscular exertion of its own ;•" 

 but which we must only look upon as another illustration of the small 

 resistance offered bythe air to the passage of a properly shaped heavy body 

 moving through it with a low velocity. 



Captain Hutton's paper was illustrated by drawings of all the 

 birds mentioned, mostly life size, executed by himself; also by smaller 

 sketches, illustrative of the flight of the Albatross. 



The President said, Captain Hutton's very interesting paper was 

 a sufficient introduction of that gentleman to the meeting. He had 

 stated what he saw himself, and therefore his communicatiou had a pe- 



