In this paper, a new graphical method, in which the stable region of the system is drawn on a plane with two of the parameters as co?ordinates, is proposed. This graphical method will be very useful in the analysis of systems with the aid of analog computers. As the stability criterion given by this method using Hermite's theorem is absolutely equivalent to that by Hurwitz'stheorem, this graphical method may be considered as a graphical representation of Hurwitz's theorem.

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In the sampled-data control for a process, whose dead time is L=lT+ti (l=0, 1, 2, …0≤ti<T, T: sampling period), L/T must be selected as an integer to obtain a shortest settling response Which has been originally proposed by A. R. Bergen and J. R. Ragazzini. However, there are several cases where this condition can not be satisfied. In those cases, hidden responses converge very slowly to steady state and sometimes hidden oscillations occur.
In this paper, the author proposes method for designating a discrete-compensator. By this method, favourite response can be easily obtained even for L/T not being an integer. Eccellence of this method is not only pointed out through several examples, but proved by experiments using a simulated process, and a discrete-compensator.

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The author has made an analog?to?digital converter, using a 4 arc 25 step rotary selector switch, relays and an electronic amplifier.Input voltages are compared with feed-back voltages, which are produced from contacts of relay switching circuits, a set of resistances and stand ard D.C.voltage.Results of comparisons sequentially control relay logical circuits, including rotary selector switch and output relays.Output informations are sent to printer or tape puncher and indicated by numerically indicating tubes.
In the case of 2-3 decimal digits conversions, sampling rate is about 1-3 per second and automatic multi-range of input is possible.

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Though the B. W. R. has been considered to be extremely safe, it is questionable whether it can be controlled in stable condition.
In this paper these problems are explained brieffy. In order to solve those problems, the control system for the B. W. R. is represented in a block diagram and analyzed by means of the analog computer.
From the analysis by the analog computer, it can be concluded that the automatic control system of the B. W. R.can work in stable conditions.

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