At that time (1864) aviation was not in public favor, and the very existence of soaring or sailing flight of birds was strenuously denied. It was held that there must be some small movements of the wings, which sustained the bird in the air, and which the observers had failed to detect, and it was not till the subsequent observations of Pénaud, Wenham, Baste, Peal, Darwin, Mouillard and others that it was admitted that a bird might sail by the sole force of the wind without flapping.
invention.psychology.msstate.edu/i/Chanute/libr...
invention.psychology.msstate.edu/i/Chanute/libr...