232 



Therefore in the case that we are supposing with the albatros 



17x58 



116x58x1800x32x0-66 



.-. x= 0-000004 nearly. 



And the resistance to the bird would be 



R = 0-000004 Av 2 

 Which is J_ of the resistance as calculated for round shot. 



150 



This difference seems very great, but several things have to be taken into 

 consideration. In the first place the resistance obtained for the albatros is 

 calculated on the supposition that both its under and front surfaces were 

 planes, which is far from being the case. The under surface of the wings is 

 concave, and perhaps offers three times the resistance of a plane surface, which 

 would greatly reduce its terminal velocity, and therefore both the velocity at 

 which the bird was compelled to fly in order to maintain its height above the 

 sea, and the resistance offered to its forward movement. On the other hand 

 the front surface is very well adapted for piercing the air, and as the resistance 

 to a round surface is only about one-third of that to a plane, and to an 

 elongated shot only one-sixth of that to a round shot, we might fairly presume 

 that these two together might reduce the resistance to one-fiftieth part of that 

 calculated for round shot. 



Again we must remember that this result is obtained by supposing that 

 the law, as determined for the velocities of round shot, holds good for lesser 

 velocities, or that the resistance always deceases as the square of the velocity ; 

 but it is well known that this is not strictly the case even with high velocities, 

 and it is probable that the law is very incorrect when the velocities, and shapes 

 of the bodies, differ very considerably. For example, the range of an ordinary 

 round shot starting with an initial velocity of 1200 or 1600 feet a second, can 

 be pretty accurately calculated by the formula here used, but in the case of a 

 mortar-shell, starting with an initial velocity of only 300 or 400 feet a second, 

 the range is much better obtained by the parabolic theory, which omits the 

 resistance of the air altogether, than by Parcelet's formula ; and the velocity 

 of the albatros is small, even when compared with that of a mortar-shell. The 

 actual resistance of the air to the bird can only be determined by accurate 

 experiments, and it is important that they should be taken, as until they are 

 completed no satisfactory conclusion can be arrived at with respect to flight. 



From the foregoing observations we can easily understand how it is that 

 the albatros never sails for long in calm weather, for when no wind is blowing, 

 its velocity over the water would be as great as that through the ah-, and it 

 would have to rush along so fast that it could not search the sea properly for 

 food, nor stop itself quick enough when it saw anything. 



I have thus endeavoured to point out what appears to me to be the only 

 possible way of accounting rationally for the wonderful flight of the albatros, 

 but once more I wish it to be understood that I by no means pretend to have 

 solved the problem, but only to have cleared the way for solving it. 



Experiments are required for determining accurately the resistance offered 

 both by the front and under surfaces of the albatros to different velocities of 

 wind, and if I should ever be in a position to undertake these, I shall not fail 

 to lay the results before the members of the Institute. 



