Thermodynamical measurement of water turbine efficiency will rather easily be brought into practice by means of thermistors used as high-sensitive thermometric elements. An idea for direct-reading efficiency meter will easily be materialized too if self-balancing d.c. potentiometer and pressure-current transmitter are available. A recorder with 0-100% efficiency scale was actually made and recently applied to a power station, where Pelton turbine runs under nearly 200m potential head and is fed with the water flow of 1.67m³/s for 2500kW generator output. When thermal disturbance was seemed to be minimum at night, test measurement was successfully made for load-efficiency characteristic curves and, as its result, was found this method compatible to conventional Pitot-tube method. Operation principle of measuring circuits and outline of field application are described, illustrated and photographed in this paper.

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Since atomic energy has been applied to a submarine, it has become necessary to know precisely the dynamic performance of a submarine navigating under water at a high speed and to improve manual controllability.
This paper treats the problems concerning adaptability of a man to submarine characteristics in case the man controls the pitching motion by means of two planes or a bow plane and a stern plane connected with each other in a fixed ratio, showing through statistic procedure an analyzing method of information transmitting gain of two meters indicating depth error and pitch angle. This analyzing method, which can be applied to measurement of the dynamic performance of a submarine, is given in appendix.

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For measurement of liquid density, the following two methods are usually adopted.
(1) To measure the apparent mass of solid with known mass m and density p, suspended in liquid.
(2) To use hydrometer.
In either method, the effect of surface tension of liquid is unavoidable.
A method reported in this paper is based on a new idea. A float with a permanent magnet is put in the liquid and another magnet (permanent magnet or electro magnet) is placed outside the liquid to suspend the float by magnetic repulsion. Theoretically, the apparent increase of mass of the outside magnet is equal to the apparent mass of the float in the liquid. This principle was proved through experiments, too.
This method is considered to be applicable to the continuous measurement of density of liquid flow in a pipeline.

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Most indicating instruments use weak spiral springs i. e. hair springs to obtain a restoration force. These hair springs have the instruments get out of order, resonating very often with external vibration transmitted to the indicating instruments. So, it is necessary to know the natural vibration of the hair springs. Given in this paper are a theoretical analysis of the vibrations of hair springs and a simple method to theoretically obtain the natural vibration, and thus, the results obtained by this method are compared with those by experiments. Vibration of hair spring induced by an external axial vibration consists of two types, one of which is an ordinary axial vibration and the other a rolling vibration of spring plane around one of its diameters. In each type, natural vibration can be easily obtained from the calculating curves proposed by the authors. Difference between calculated values and experimental ones are merely a few percent.

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Generally, it is difficult to govern the speed of gasoline engine compared with that of diesel engine because of parametric change.
Reported in this paper is an experimental study of gasoline engine of Wisconsin VE-4 power unit.
In this experiment, a ball governor equipped with power unit was used and in addition, a simple discontinuous governing technique was applied.
The speed governing was extremely difficult affected by the inertia of D.C. generator as the load.
The ball governor satisfactorily operated for this inertial load, proving that it is available for all kinds of loads to be used as power unit.
On the other hand, discontinuous governing was not successfully applied due to the effects of parametric change (especially throttle sensitivity) and larger load inertia. As its technique is now being improved, its experiment shall be reported in the next paper.

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