RELATION OF SIZE AND WEIGHT TO FLIGHT. It is an interesting question whether or not tho ani mals that fly represent the limits of size and weight attainable by living creatures. The al batross, condor, swan, and pterodactyl represent the maximum of weight, but these range only from 15 to 30 pounds, and the spread of wings is but 7 feet in the swan, 8 to 10 feet in the condor, and 10 to 14 feet in the albatross. The very largest examples of pterodactyls had a spread of wing of 20 feet; but owing to the small size of the body and wonderful lightness of the skeleton, their weight at the outside was not more than 30 pounds. These reptiles, with their great expanse of wing, offer one of the excep tions to the general rule that the wing area per pound is proportionally less in ani mals than in small, a seeming anomaly which, though imperfectly understood, is partly based on the fact that the great sweep of a large wing makes it much more effective than one of small dimensions. Very erroneous ideas prevail both as to the power of the muscles and the speed attained by birds. Marcy long ago showed that
the contractile power of the muscular fibres was certainly no greater in birds than in mammals, and observation has shown that even ducks, which fly very rapidly, seldom attain a greater speed than 35 to 40 miles an hour, although under favorable conditions some species may exceed this.
It has long been evident that if the problem of artificial flight is solved it will be by a system of planes imitating the methods employed in sailing flight, and all recent experiments have been conducted on this line. But while there have been many different theories to explain the principle of soaring or sailing. many of them fanciful and some based on misinterpretations of facts, the subject is far from being under stood, although the researches of Langley, Maxim, Chanute, and Lilienthal have thrown much light upon it.