Neither birds nor any creatures that live or have lived afford us any criterion as to the limit of size that must be placed on an aeroplane. The largest of whales is weak and insignificant beside an ocean liner, and the condor and albatross, with their spread of ten or twelve feet and weight of ten to twenty pounds, tell us nothing of what may be the possibilities of size and weight. Among the various problems confronting the would-be navigator of the air is that of at times making headway against a medium moving at the rate of ten, twenty, or thirty miles an hour, sometimes even more, a difficulty that neither locomotive nor steamer is called upon to meet. True, an aeroplane would, to use a technical term, probably lie within two and one-half points of the wind and could thus advantageously beat to windward, but any deviation from a straight course means loss of time, and nowadays time is everything. The mode of propulsion may be, undoubtedly will be, as entirely different from a wing as the propeller is unlike the tail of a fish, and as the study of fish has thrown little or no light on the problems of the proper form or best motor for a ship, it is doubtful if the study of birds will do more for the aerodrome. Nor does it seem likely that a study of the bird will suggest any new devices in the way of joints, braces, or rudders, for what must be discouraging to those engaged in solving the problems of flight is the utter inadequacy of the bird’s wing, from a mechanical standpoint, for the work it is called upon to do, for in all its articulations there is a freedom of movement, an amount of play that would be inadmissible in any machine. The shoulder, elbow and wrist joints are but loose affairs, depending for their efficiency on the pull of the muscles; subtract the element of life from the wing of a bird and it becomes at once limp and useless. And herein is the key to the bird’s success as a flying machine; it has _life_, and while the wing may reveal certain principles of balancing, it cannot teach us all the art, for it is done instinctively. The bird has back of it untold ages of experience and its actions during flight demand no thought; the muscles respond instinctively to each change in the pressure and direction of the wind, and the bird need take no thought as to how it shall fly.