involved in the Sailing Flight of the Albatros. 131 



flight) has recently been very ably and fully discussed by the 

 Duke of Argyll in ' The Reign of Law/ and by Dr. Pettigrew in 

 the Transactions of the Linnean Society, vol. xxvi. ; the second, 

 however, as far asIknow,has never been attempted; and 1 propose 

 therefore to make a few remarks on the "sailing" flight of the 

 Albatros (Diomedea exulans, L.), and try to determine approxi- 

 mately the probable resistance of the air in order to allow it to 

 sail for half an hour without moving its wings. Before com- 

 mencing, however, it may be necessary to remark that the velo- 

 cities spoken of are velocities of the bird through the air, and not 

 over the water ; for the latter will be very different when a wind 

 is blowing. 



I estimate the under surface of the wings, body, and tail of 

 the Albatros to be about 8 square feet (see fig. 1) ; and if we take 



Fig. 1. 



the weight of the bird to be 16 lbs., we find that it would take a 

 pressure of 2 lbs. per square foot to support it in the air. This 

 pressure would be given by an upward current of air having a 

 velocity of 31 feet a second if the surface acted upon were flat : 

 but the wings of the bird when sailing are bent downwards (see 

 fig. 2), which would increase the resistance; on the other hand, 



Fig. 2. 



the body of the bird is convex, and the wings are inclined at an 

 angle to the horizon, both of which would decrease the resist- 

 ance, while the surface of the wings is about three times as large 

 as the surface of the body and tail. Balancing one against the 

 other, we perhaps shall not underestimate it if we take an up- 

 ward current of air with a velocity of 30 feet per second as suffi- 

 cient to support it. This, in other words, means that on a per- 

 fectly still day an Albatros with its wings outstretched, but with 

 no forward movement, would fall downwards at a constantly in- 

 creasing rate until it had attained a velocity of 30 feet per second, 



K2 



