The Turbina was driven by a number of steam-turbines that worked a good deal like the water-turbines that use the power of Niagara. Just as a water-wheel is driven by the weight or force of the water striking the blades or paddles of the wheel, so the force of the many jets of steam striking against the little wings makes the wheels of the steam-turbines revolve. If you take a card that has been cut to a circular shape and 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 whirling in the breeze.
To stop the Turbina was an easy matter; Mr. Parsons had only to turn off the steam. But to make the vessel go backward another set of turbines was necessary, built to run the other way, and working on the same shaft. To reverse the direction, the steam was shut off the engines which revolved from right to left and turned on those designed to run backward, or from left to right. One set of the turbines revolved the propellers so that they pushed, and the other set, turning them the other way, pulled the vessel backward—one set revolving in a vacuum and doing no work, while the other supplied the power.
The Parsons turbine-engines have been used to propel torpedo-boats, fast yachts, and vessels built to carry passengers across the English Channel, and recently it has been reported that two new transatlantic Cunarders are to be equipped with them.
A few years after the Pilgrims sailed for the land of freedom in the tiny Mayflower a man named Branca built a steam-turbine that worked in a crude way on the same principle as Parsons's modern giant. The pictures of this first steam-turbine show the head and shoulders of a bronze man set over the flaming brands of a wood fire; his metallic lungs are evidently filled with water, for a jet of steam spurts from his mouth and blows against the paddles of a horizontal turbine wheel, which, revolving, sets in motion some crude machinery.
There is nothing picturesque about the steel-tube lungs of the boilers used by Parsons in the Turbina and the later boats built by him, and plain steel or copper pipes convey the steam to the whirling blades of the enclosed turbine wheels, but enormous power has been generated and marvellous speed gained. In the modern turbine a glowing coal fire, kept intensely hot by an artificial draft, has taken the place of the blazing sticks; the coils of steel tubes carrying the boiling water surrounded by flame replace the bronze-figure boiler, and the whirling, tightly jacketed turbine wheels, that use every ounce of pressure and save all the steam, to be condensed to water and used over again, have grown out of the crude machine invented by Branca.
As the engines of the Arrow are but perfected copies of the engine that drove the Clermont, so the power of the Turbina is derived from steam-motors that work on the same principle as the engine built by Branca in 1629, and his steam-turbine following the same old, old, ages old idea of the moss-covered, splashing, tireless water-wheel.