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Art. LIX. — On the Mechanical Principles involved in the Sailing Flight 

 of the Albatros. By J. S. Webb. 



[Read before the Otago Institute, November 2, 1869.] 



In the first volume of the " Transactions of the New Zealand Institute," there 

 is an abstract of a paper by Captain Hutton on this subject, but for want of 

 necessary type for the algebraic formulae the paper could not be printed in full. 

 A revised and modified copy of the more important portions of it has, however, 

 been published in the " Philosophical Magazine " for August last. The subject 

 dealt with by Captain Hutton is what has been, somewhat inappropriately, 

 called the "Sailing flight of the Albatros " — that steady and continued motion, 

 without any observable action of the wings, which has attracted the attention 

 of every one who has made a voyage in the southern seas. The paper is ably 

 written and very interesting, but in his mathematical treatment of the subject 

 Captain Hutton has not been happy, having as it appears to me, made a mis- 

 take at the outset of his calculations. The object of the present communi- 

 cation is to supply what I consider to be the necessary corrections, and to show 

 the effect which the new results thus arrived at have upon the general conclusions 

 drawn by Captain Hutton from his own calculations. As I cannot ask this 

 meeting to follow me through a dry, though by no means abstruse, process of 

 mathematical reasoning, I have thrown that portion of the paper into the form 

 of an appendix, which I lay on the table for perusal of those members who 

 may be desirous of examining it. 



In his paper* Captain Hutton proposes to himself " to determine approxi- 

 mately the probable resistance of the air in order to allow ' the albatros ' to sail 

 for half an hour without moving its wings." He estimates the under surface 

 of the wings, body, and tail, at 8 sq. ft., and the weight of the bird at 16 lbs. 

 From these data he concludes that "if an albatros starts with a velocity of 

 115 feet per second, it could maintain a constant height above the sea until its 

 velocity was reduced to 64 feet per second, by merely increasing the angle to 

 the horizon at which it was flying from 0° to 7°." He assumes that the wings 

 are always inclined 15° more than the body of the bird. The corrections I 

 offer to-day show that, on the data assumed, the velocity at starting must be 

 155 feet per second, instead of 115, and that it must not be reduced during 

 the interval below 100 feet per second, instead of to 64 feet. 



A consideration of the following extract from Captain Hutton's paper 

 will show the bearing of this correction on his general results. " The velocity 

 of the air in a ' fresh sailing breeze' is about 30 feet per second, in a 'moderate 

 gale' 60 feet, in a 'strong gale' 90 feet, and in a 'great storm' 120 feet per 

 second. Now, an albatros can often be seen sailing, though slowly, directly 

 against a strong gale : his velocity " (through the air) " must therefore often be 

 more than 90 feet per second. He is however most at home in a strong breeze 

 or moderate gale, when the velocity of the wind is 50 or 60 feet per second, 

 and consequently when his velocity would have to be 70 or 80 feet per second 

 to enable him to fly easily against it. In a calm or light air, when the wind 

 has a velocity of only 10 feet per second, the albatros rarely sails for so long 

 as a minute at a time, — the reason for this being that as, in order to sustain 

 himself in the air he must move through it with a velocity not less than 

 64 feet per second, he would even when flying against it have to travel over 

 the sea at the rate of not less than 54 feet per second, or 36 miles an hour, and 

 so could not reach it for good, or stop himself quickly enough when he saw 

 anything ; so that the velocity and manner of flight observed in the albatros 

 correspond closely enough with those calculated as necessary from theoretical 



* "Phil. Mag.," Vol. xxxviii., p. 130.— (No. 253, August, 1869.) 



