Note 17 — Chapter II · PRELIMINARY

Observers following de Lucy have long since called attention to the fact that as the scale of Nature’s flying things increases, the size of the sustaining surfaces diminishes relatively to the weight sustained. M. Harting (Aeronautical Society, 1870) has shown that the relation √area/weight is surprisingly constant when bats varying in weight as much as 250 times are the subject of the experiment, and later observations by Marey have not materially affected the statement. As to the muscular power which Nature has imparted with the greater or lesser weight, this varies, decreasing very rapidly as the weight increases. The same remark may be made apparently with at least approximate truth, with regard to the soaring bird, and the important inference is that if there be any analogy between the bird and the aerodrome, as the scale of the construction of the latter increases, it may be reasonably anticipated that the size of the sustaining surfaces will relatively diminish rather than increase. We may conveniently use M. Harting’s formula in the form a = n2w(2/3) = l2m2 where a = area in sq. cm., w the weight in grammes, l the length of the wing in cm., n and m constants derived from observation.