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 power developed by the "Mauretania" and "Lusitania." The aggregate power of Parsons' turbines fitted for marine propulsion up to date is six million shaft horse-power. This embraces ships of practically all nationalities. The power of turbines of the same type made for generating electricity and other duty on land is also about six million shaft horse-power—considerably more than the available power of Niagara Falls. The diagrams on the four preceding pages indicate the size of ships fitted at different successive periods for the Royal Navy and for the merchant marine.

The marine turbine, with the modifications we have so far described, is only suitable for vessels of over 16 knots speed, and to extend its use to vessels of a less speed than this, which comprise two-thirds of the tonnage of the world, has been our constant aim. The first plan for the attainment of this end is somewhat in the nature of a compromise, and is called the combination system, because the reciprocating engine is used to take the first