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Rh that the efficiency is a maximum when the vane speed is half that of the jet. It will also be seen that the maximum efficiency is only 50 per cent., which is all that can be attained with a flat plate. This loss of efficiency is due to shock, and to the fact that the jet moves on with the wheel, and the energy which it still contains is not utilised.

Fig. 6. -- Action of Curved Blades.

The first loss can be avoided by curving the vane as shown at A,fig. 6, which gradually changes the direction of flow of the jet. If matters are so arranged that the direction of flow, of the jet is completely reversed as at B, fig. 6, it is clear that the energy abstracted will be the maximum possible; and if the vane speed is, as before, half that of the jet, the efficiency becomes 100 per cent. In practice, however, owing to the necessity of arranging for Rh