The close analogy between the laws for the flow of steam and water under small differences of pressure have been confirmed by experiment, and the usual formula of velocity = √2gh, where h is the hydraulic head, gives the velocity of issue from a jet for steam with small heads and also for water, and I shall presently follow this part of the subject further in dealing with the design of turbines. Having decided on the compound principle it was necessary to commence with small units at first; and thus, notwithstanding the compounding, the speed of revolutions though much reduced was still rather high.
The first compound steam turbine of 10 horse power (page 7) ran at 18,000 revolutions per minute, and had slightly elastic bearings to allow it to rotate about its dynamic or principal axis. The turbine teeth or blades were like a cog wheel, set at an angle and sharpened at the front edges, and the guide blades were similar. These are shown in Fig. 6 on the next page.
Gradually the form of the blades was
