THE ALBATROSS. 



213 



" 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 demonstrated by means of a pen- 

 dulum, composed of a metal ball, suspended by a long 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 resistance of the sand which the point of the pendulum had to cut through 



ALBATROSS. 



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. For 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 necessary to give a bird momentum sufficient to 

 overcome resistance for a certain time, and wings are required of sufficient expanse to support it as it 

 sails slowly through the air. These conditions are admirably carried out in the Albatross. Its expanse 

 of wing is perhaps greater than that of any other bird, and its weight, 15 Ibs. and upwards, is 

 very large. Its shape also, when the neck is stretched out as in flying, approaches nearly to that of 

 Newton's solid of least resistance, while more than one voyager has remarked the slowness with which 

 it sails past. 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 ten minutes ; while the Albatross, as I 

 have before mentioned, sails sometimes for an horn*." 

 170 



