"Present day knowledge of both the theory and the technique of steam engines has justified Watt in the principles which he laid down, which were that the greater the steam pressure and range of expansion, the greater will be the work obtained from a given weight of steam, and that the cylinder should be kept as hot as the steam which enters it. The main development of the steam engine since his time has consisted in an extension of the range of expansion and in an ever increasing degree of compounding. The separation of the condenser from the cylinder by Watt was followed by the division of the expansion into stages in separate cylinders, finally into four stages in the highest development of the reciprocating engine. The steam turbine carries this subdivision still further, the number of stages included in a reaction turbine of high efficiency being commonly sixty or more."