cut the edges so that little wings will be made, then blow on this
winged edge, the card will revolve with a buzz; the Parsons
steam-turbine works in the same way. A shaft bearing a number of steel
disks or wheels, each having many wings set at an angle like the blades
of a propeller, is enclosed by a drumlike casing. The disks at one end
of the shaft are smaller than those at the other; the steam enters at
the small end in a circle of jets that blow against the wings and set
them and the whole shaft whirling. After passing the first disk and its
little vanes, the steam goes through the holes of an intervening fixed
partition that deflects it so that it blows afresh on the second, and so
on to the third and fourth, blowing upon a succession of wheels, each
set larger than the preceding one. Each of Parsons's steam-turbine
engines is a series of turbines put in a steel casing, so that they use
every ounce of the expansive power of the steam.

It will be noticed that the little wind-turbine that you blow with your
breath spins very rapidly; so, too, do the wheels spun by the steamy
breath of the boilers, and Mr. Parsons found that the propeller fastened
to the shaft of his engine revolved so fast that a vacuum was formed
around the blades, and its work was not half done. So he lengthened his
shaft and put three propellers on it, reducing the speed, and allowing
all of the blades to catch the water strongly.

The _Turbina_, speeding like an express train, glided like a ghost over
the water; the smoke poured from her stack and the cleft wave foamed at
her prow, but there was little else to remind her inventor that 2,300
horse-power was being expended to drive her. There was no jar, no shock,
no thumping of cylinders and pounding of rapidly revolving cranks; the
motion of the engine was rotary, and the propeller shafts, spinning at
2,000 revolutions per minute, made no more vibration than a windmill