BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertically sectional side view of fans of cascade connection of the present invention with a portion being cut away.
FIG. 2 is a front view of the fans shown in FIG. 1.
FIG. 3 is a front view of a commutation device in the fans of cascade connection of the present invention.
FIG. 4 is a perspective view of the commutation device of FIG. 3.