69 the lines h 1 and h 2 are perpendicular to all segments of the airstream passing through them these lines are nearly straight but are slightly bowed to the left as viewed in fig3 similar lines can be drawn at locations intermediate the lines h 1 and h 2 in order for the channels 75 to be constant velocity channels it is necessary that h 2 be greater than h 1 and that any h line radially inwardly of the line h 1 be greater than h 1 more specifically it can be shown that the relative velocity of air passing through the rotor channel 75 varies inversely with the distance from the rotational axis 67 thus w 1 w 2 r 2 r 1 where w 1 is the air velocity relative to the rotor at the radial outward port 77 w 2 is the air velocity relative to the rotor at the radial inward port 79 and r 1 and r 2 are the radial distances from the axis 67 to the outer and inner peripheries of the centers of lines h 1 and h 2 respectively accordingly if the rotor channels 75 were of constant cross sectional dimensions throughout the change of radius would cause air expansion as the air enters the rotor through the rotor channels 75 and air compression as the air leaves the rotor cascade to compensate for this i e to have w 1 w 2 it is necessary to adjust the spacing or h distance between adjacent pairs of rotor blades 69 in accordance with the formula r 1 h 1 r 2 h 2 the stator blades.