466 Proceedings. 
tive degrees of inertia of a body, proved that in all cases 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, ha¥ing a uniform direction, affording no opportunity, as in the case 
of the ship, of oe 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 
formule, 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 formule, 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 =e of five and ten degrees to the horizon, at fifty-eight and twenty-nine 
y, showed that it would be able to sail only about eight minutes, 
5 dieta dpud as long as the albatros, the resistance of the air being in à 
= similar ratio i in both cases. However, the pigeon could not sail so long as 
ee without = carried away fed the "i the bird would 
