ClipArt ETC
"If a jet with the velocity V strikes the bucket at an angle a, its velocity A B could be resolved into two components —one C B at right angles to the shaft, and one C A parallel to the shaft. The one at right angles to the shaft, commonly known as the velocity of whirl, would produce a rotative impulse equal to Vcosa, and V1, the velocity of the vane necessary for maximum efficiency." —Derr, 1911

Jet Steam Stream Hitting Curved Vane

"If a jet with the velocity V strikes the bucket at an angle a, its velocity A B could be resolved into…