Fig. 3. (A) A frog gliding through the air; the airflow with respect to the frog is parallel to the frog's flight path, but in the opposite direction from that in which the frog is moving. The angle of the frog's glide path with respect to the horizontal is called the glide angle, . The angle that the frog's cranial—caudal axis makes with the frog's glide path is called the angle of attack, . (B) If a wind-tunnel is tilted to the glide angle of a frog, the airflow past a frog that is stationary in the working section of the wind-tunnel simulates the airflow relative to a frog gliding at that angle through still air. Air is blown by a 560 W fan through the transparent test section of the wind-tunnel, measuring 38 cm high, 38 cm wide and 46 cm long. The tunnel can be tilted to blow air at any orientation ranging from vertical to horizontal. The tunnel airspeed was continuously adjustable up to 18 m s^-1. Observations of Polypedates dennysi gliding in free air and in the wind-tunnel show that this species glides at a glide angle of 45° and an airspeed of approximately 13 m s^-1.