Summary of the Negotiation with British General Post Office about the Submarine Cable by Kenjirō Den, No Date. JACAR (Japan Center for Asian Historical Records National Archives of Japan) Ref. B04011012400 (7-15), Taiwan Hong Kong Kan Kaitei Densen Chinsetsu Ikken, (1-7-4) (Gaimushō Gaikō Shirōkan, Japan).

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