4iQ6 Proceedings. 



tive degrees of inertia o£ a body, proved that in all eases the bird would 

 reach the water in a curved line, at a certain distance behind its first posi- 

 tion ; and concluded that the common notion, that a certain position of the 

 bird's wings and feathers enabled it to sail against the wind, was erroneous, 

 and opposed to the known laws of physical science. He also combated the 

 theory that an albatros could fly almost against the wind in the same manner 

 that a ship beats to windward, pointing out that in the one case the pressure 

 of the wind was resolved in forces, having other directions, by the resistance 

 it received from the water ; whereas the albatros was placed in only one 

 medium, having a uniform direction, affording no opportunity, as in the case 

 of the ship, of resolving its direction into that most advantageous to itself, 

 viz. forwards. 



The author then propounded his own theory, that the albatros receives mo- 

 tion by means of the momentum it has previously acquired by strokes of its 

 wings in the air, or of its feet in the water, or both combined. He then 

 went on to illustrate that duration of sailing might be supposed to depend 

 upon the relative momentum and resistance. He showed, by algebraic 

 formulae, that a velocity, at starting, of 116 feet a second, sailing at an angle 

 of five degrees to the horizon, would enable the bird — by gradually increasing 

 the angle at which he was flying to ten degrees — to maintain a uniform 

 height until its velocity was reduced to 58 feet a second. He then went on 

 to show, by means of comparing the resistance offered to a round shot, the 

 amount of resistance required to allow an albatros to sail for half an hour 

 without employing his wings, and only reducing his velocity from 115 to 58 

 feet per second. He allowed 0'16 square feet as the effective area of resist- 

 ance to the forward progress of the bird; and, by ably arranged and 

 accurately defined formulse, arrived at the conclusion that the resistance 

 would be much less than one-fortieth of that calculated for round shot. He 

 also showed that the greater the weight of the bird, and the smaller the 

 velocity at which it was compelled to fly in order to maintain its position in 

 the air, and the less the front area, the greater would be the period during 

 which the bird could sail without using its wings. Thus, it might be said 

 that the sailing power of a bird depended upon its weight, resistance to 

 the downward force of gravity being great, while the resistance to its forward 

 movement was small. He then took a Cape pigeon as an illustration ; and 

 calculating its terminal velocity at 10 feet a second, and the rate of flying at 

 an angle of five and ten degrees to the horizon, at fifty-eight and twenty-nine 

 respectively, showed that it would be able to sail only about eight minutes, 

 or one-fourth as long as the albatros, the resistance of the air being in a 

 similar ratio in both cases. However, the pigeon could not sail so long as 

 eight minutes without being carried away by the wind, as the bird would 



