This may be hard to express without a diagram. For the beam that split left and came back towards the half silvered mirror perpendicular to the aether wind, shouldn't it be solved that way vectorially? My textbook has the speed of light (c) as the hypotenuse. Which has screwed me over in the way I think of it. Shouldn't the resultant velocity be the hypotenuse as the wind and the light beam meet at a right angle?