Birds inhabiting the Southern Ocean. 295 



as the mean winter temperature of lat. 50"^ S. is about 50° F. 

 The bird, therefore, could not raise the temperature of the air 

 taken into these cells more than 60° F. This would increase 

 its volume not quite one-eighth ; and taking 100 cubic inches of 

 air to weigh 31 grains, and the average weight of an Albatros 

 to be 17 lbs., as given by Gould, it would be necessary, in order 

 that the specific gravity of the bird might be brought to that of 

 the atmosphere, that these cells should contain 1,820 cubic feet 

 of air; or, in other words, they must be more than 1,200 times 

 the size of the body itself of the bird, which, to say the least, 

 would give it when flying an aldermanic appearance, which I 

 have never observed. In fact, it would require a sphere of more 

 than fifteen feet in diameter to contain the necessary quantity 

 of air. Even if it could thus buoy itself up, it would entirely 

 defeat its own object ; for it would at once destroy the whole of 

 its momentum, and, unless propelled forward by its wings, 

 would drift helplessly to leeward. However, I do not wish it to 

 be inferred that I consider the air-cells of no use. The greater 

 portion of them are situated round the neck, wings, and fore- 

 part of the body of the bird, and I believe that by their means 

 he is enabled to shift slightly the position of his centre of 

 gravity, and thus, with very slight muscular exertion, to vary 

 the inclination of his body to the horizon, according to the rate 

 at which he is moving through the air. 



Dr. Bennett, in his ' Gatherings of a Naturalist ' (p. 78), gives 

 a diagram explanatory of the flight of the Albatros ; and, if I 

 understand him rightly, says ( Ibis, 1862, p. 90) that it cannot 

 sail* directly against the wind, but only in the way which sailors 

 call "close-hauled." This diagram represents a square-rigged 

 ship sailing six points from the wind, a cutter sailing four and 

 a half points, and an Albatros flying two points from the wind ; 

 from which I infer, although he does not expressly say so, that 

 he considers that the wind helps forward the Albatros in the 

 same way that it does the ships. But that this is erroneous is 



* In this paper I use the word " sail," for want of a better one, to denote 

 the power these birds possess of flying for a considerable time without 

 moving their wings, and the following remarks relate to this mode of fly- 

 ing only. 



