34 Captain F. W. Hutton on the Mechanical Principles 



If we take A, in the case of the Albatros, to represent one 

 square foot, and put the other values into the equation, we get 



16x51 



115x64x32x1800x1' 



= 0-000002 ; 



so that the formula for the resistance of the air to the Albatros 

 ought to be 



R= 0-000002 v\ 



The formula given by Poncelet for the resistance to round shot is 



R = 0-0006 Av 2 . 



If, therefore, these calculations are tolerably correct, the resist- 

 ance offered to the Albatros must be 3 ^q of that offered to round 

 shot. This at first sight seems to be impossible ; but I must 

 remark, first, that the terminal velocity of the bird may be less, 

 and the angle at which it flies to the horizon greater than those 

 that I have taken, either or both of which would reduce the ve- 

 locity at which it was compelled to sail in order to support itself 

 in the air ; secondly, that the resistance of the air to the flight of 

 elongated projectiles seems to be very much less than that to 

 round shot ; but I have seen no experiments on the subject ; 

 and as the shape of the Albatros is perhaps the best that could 

 be devised for penetrating the air (see fig. 1), the resistance it 

 had to overcome would undoubtedly be considerably less than 

 that offered to the best-shaped projectile ; and thirdly, that the 

 formula, as obtained by experiment, for round shot does not pre- 

 tend to absolute correctness, and applies to projectiles starting 

 with an initial velocity of 1200 feet a second ; and it is highly 

 probable that the law that the resistance decreases as the square 

 of the velocity does not hold good for small velocities such as 

 those we are now considering. For example, the range of the 

 larger mortar-shells, which start with an initial velocity of 300 

 to 400 feet per second, is much more truly calculated by the pa- 

 rabolic theory, which omits the resistance of the air altogether, 

 than by allowing for it by means of the formula 11 = 0*0006 A?; 2 . 

 Still the resistance to the Albatros seems very small, and it 

 would be interesting to try to obtain it experimentally. From 

 formula (1) we obtain 



W(V-v) 



Y.v.g .k .A 



by which we see that weight is necessary for a bird to be able to 

 sail, and that the greater the weight the longer it can continue to 

 sail ; but I cannot agree with the Duke of Argyll (Reign of Law, 



