1) Evidence - The plane ride is remarkably smooth. Statement - You do not feel the sensation of being thrown from your seat.
2) Evidence - Speed is difficult to detect in the air. Statement - You perceive no change in the pressure of the wind on your face.
3) Evidence - The plane requires two people for flight. Statement - An assistant who has been holding the machine in balance on the rail starts forwards with you.
4) Evidence - Air movement affects flight. Statement - The machine is placed upon a single-rail track facing the wind.