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ANALYSIS OF MR CHARLES SELLS EXPERIMENTS. 223

these two screws proved to be highly efficient, and these results would
seem to be confirmed by the experiments made by the Admiralty on
H.M.S. "Emerald" in 1863, when general efficiency of 0'466 was
shown when running with a six-bladed screw as against 0"457 with a
four-bladed and 0'422 with a two-bladed common screw. In previous
trials on H.M.S. "Shannon" in 1862 with propellers on Woodcroft's
principle, the general efficiency with the six-bladed was 0*420 as
against 0'445 with a four-bladed and 0*409 with a two-bladed common
screw ; but in this case the surface of the six-bladed was very
excessive, being 172'8 square feet as against 115*2 of the three- and
71'2 of the two-bladed screws.
