There is a wind tunnel made of glass. It's set horizontally (Air is moving horizontally). Plane waves of light are coming from just above. These waves may transmit the roof of the wind tunnel horizontally and may reach the floor of the wind tunnel horizontally also. But how about the light ray ? Light ray may not be 90 degrees (with light waves) to an observer who is at a standstill relative to the wind tunnel. From this angle (not 90 degrees), the speed of the air may be determined. In the aether (of outer space), it may be the same.