THREE different methods are available for the measurement of the performance of a steam engine, and serve that purpose from different points of view according to the particular feature of merit it is desired to emphasise. Thus, from the point of view of the manufacturer whose aim is to produce a turbine of the highest efficiency, that is, one which will convert into useful work the highest possible proportion of the pressure energy that is available in the steam, a figure expressing this proportion appears to meet the requirements of the case. This figure is almost (that is, except for the work of restoring the water of condensation to. the boiler) identical with the ‘efficiency ratio’ as defined by Willans and Sankey in terms of the Rankine cycle, a ratio for many years accepted as the criterion of merit of a steam engine. The user of a turbine, on the other hand, is not so interested in what may be called the intrinsic efficiency of the engine, as in knowing how many pounds of steam per hour he has to generate in his boilers in order to produce a horsepower or kilowatt of output; consequently, a more significant expression of the engine's efficiency from his point of view is the consumption in pounds of steam per horse-power hour, under standard conditions of steam generation.