It is very remarkable that the steam turbines have made rapid strides during last ten years, and are still improving with everprogression. Of the two main classes of the turbines, the impulse and the reaction, with their respective merits, it is very difficult to ascertain which is superior to the other. The writer will discuss the merits of the two classes from the following standpoints. (1) Impulse turbine blade efficiencies. We can calculate the efficiencies diagramatically, but at the same time we must consider the effect of the residual energy from the preceding stage and the two efficiencies with and without exit energy have to be calculated. This shows a great difference between them. And by this latter efficiency we can increase the available energy in a turbine by the amount L(1-η/ηe), in which L is the liberated energy in a stage, η & ηe the efficiencies with and without utilization of energy from the preceding stage. But to have the effective utilization of the exit energy, we must pay attention to the followings. (A) Critical pressure through nozzles for steam with entrance energy (B) Nozzle inlet angle to correspond the exit direction of steam from the preceding stage. (C) The ratio of nozzle height to blade height. (2) Impulse blade stress and rear coefficient. We take the stress of blades due to centrifugal force and define the ratio of the peripheral speed of blades to the actual steam speed from nozzles as rear coef. We will find a formula containing the stress, the steam quantity through the blades and revolution of the turbine. By this formula we may conveniently find the capacity and sizes of the turbine corresponding to the given data. (3) Reaction turbine efficiencies. We have efficiency curves deduced from the experiments obtained at Parsons' Works, but the effect of the loss due to tip leakage on these good efficiencies is not negligible which can not be avoided in the reaction turbine construction. The leakage amount through the clearauces can be easily calculated by the formula given in the Prof. Goudie swork. The steam through blades and clearances is greately affected from whirling and eddies due to the clearances. By these evil effect on the steam, the efficiencies of reaction blades are greately reduced. The loss of the efficiency is found almost twice that of the ratio of the quantity of steam through the clearance to the quantity through blades. (4) Reaction blade stress and rear coefficient. The meanings of the term are same as above. In order to compare the capacities of the two classes, we take the velocity ratio of reaction blades to have the same efficiency as in the impulse blades and find a formula. The two formulae of the rear coefficients of impulse and reaction blades show that the latter surpass the former in the capacity of the turbines.

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The best velocity in the spiral casing the section of which is circular may be found by the equation Aλ+Bλ^<3/2>-1=0, where λ is the coefficient of casing velocity. This equation can be represented by a diagram which for all practical purposes may be used to determine the best casing velocity with an error of ±4 percent in the worst case, which can be corrected more accurately, if desired. The range of merit of making the throat conical can be determined by the equation Aλ^2+0.83Bλ^<5/2>-2λ+∧_<k=1>=0. This is also represented by a diagram, by which the limit of selection of the casing velocity for a certain area ratio of the conical throat can be known.

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