**Nakashima Akira**

1908〜1970

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1908〜1970

Nakashima Akira was born on January 5, 1908, and graduated from Electrical Engineering Department, School of Engineering of Tokyo Imperial University. Immediately after the graduation, he joined Nippon Electric Company (NEC), where he was assigned to design relay circuits to be used for remote sensing and control, automatic telephone exchange, etc. at Research Department headed by Shimazu Yasujiro. In those days, relay circuit design was done based on a sort of inspiration of talented design engineers. Therefore, in the field of cable communications, exchange engineers designing relay circuits were regarded as temperamental artists, while transmission engineers as intellectual people. In this environment, Nakashima endeavored to enable relay circuit design done theoretically by determining the basic properties of relay circuits, and by expressing them in suitable mathematical forms. This was the motive Nakashima launched the research on the branch of science that is now called switching theory.

Nakashima began his research with investigating various relay circuits designed by his predecessors and extracting from them common patterns and accepted methods. He built his theory based upon the fact that each relay contact has impedance that is a function of time whose value shall be limited to either zero or infinite. He represented impedances of relay contacts by symbols such as A, B, and C. Then he could represent the impedance of the connection of two contacts, A and B, in series by A+B, and the one in parallel by AxB. He also employed the symbol '=' to represent the equivalence of two impedance functions. By assuming symbols + and x that represent connections to be arithmetic operators, he arrived at an algebra whose arithmetic rule was totally different from the one of the conventional algebra (It was several years later that Nakashima realized that the algebra he had arrived at was the Boolean algebra). With the use of this new tool, he could establish the theory of the equivalent conversion between two-terminal relay circuits.

In 1936, soon after he began the above research, Nakashima was transferred to transmission engineering, and he could continue his research only at night at his home, encouraged by Niwa Yasujiro, NEC's Chief Engineer and Hanzawa Masao, one of his colleagues who remained with the exchange engineering. However, after Japan entered the Second World War, Nakashima was further transferred to radar and wireless communication engineering, where he had to work much overtime and even on holidays, and he could no longer continue his research.

After the war, Nakashima was appointed a Managing Director of NEC. He was then transferred to Ando Electric Co., one of NEC's subsidiary companies, as its President. He remained in that position until he died on October 29, 1970 at the age of 62.

（Takahashi Shigeru）

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