A Qing dynasty volume with a yellowed title page in bold, black characters from the 1760s about Ryukyuan students sits on display in a glass case at the Imperial College in Beijing on Wednesday. Chinese scholars say that the 18th century book is evidence that the Diaoyu Islands are part of China's territory. Photo: AFP
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In 1893, the Empress Dowager Cixi granted the Diaoyu Islands to Sheng Xuanhuai who was the Chief Minister of the Court of Imperial sacrifices at that time. Being also a businessman in the pharmaceutical sector, he was keen on harvesting the plant statice arbuscula on the islands. The Chinese used these herbs to manufacture pills to prevent high blood pressure and relieve pain because of dampness. Being thrilled about the effectiveness of the pills the Dowager Cixi awarded three of the disputed islands to the Chinese pharmacologist.251 This decree carried the imperial seal thereby making it official: The medical pills submitted by Sheng Xuanhuai have proved to be very effective. The herbs used in making the pills are said to have been collected from the small island of Diaoyutai, beyond the seas of Taiwan. It has come to my knowledge that the said officials family has maintained for generations pharmacies offering free treatment and herbs to destitute patients. This is really most commendable. The three islands of Diaoyutai, Huangwei Yu, and Chiwei yu are hereby ordered to be awarded to Sheng Xuanhuai as his property for the purpose of collecting medicinal herbs. Seal of Queen Mother Cixi
By virtue of this imperial act the three mentioned islands could have become Chinese property. At least the Qing Dynasty recorded officially the existence of the islands.
Until the 1894, the Japanese could not make any progress regarding the incorporation of the islands. In a letter of response to the Director of the Prefecture Administration Bureau of the Ministry of Home Affairs Egi Kazuyuki the Okinawa Prefecture Governor stated that no investigation had been carried out so far on the islands. In his request, Mr. Kazuyuki wondered as well whether there was evidence such as old records or folklore that demonstrate the islands belong to our country. The answer of the Okinawa Prefecture was the following:
there exist no old records related to the said islands or any transcribed evidence or folklore and legends demonstrating that the islands belong to our territory
This secret letter conveys a different idea of what is the official Japanese contention published on the web page of the Japanese Foreign Ministry
* The advent of the Sino-Japanese War was instrumental for the Japanese government regarding the incorporation of the Senkaku Islands. The long awaited suitable moment had finally arrived. After the outbreak of the war on August 1rst, 1894, Chinas military defeat enabled the Japanese Tenno to impose harsh peace condition upon the struggling Qing Dynasty. China lost its territory in Taiwan and on the Liaodong peninsula.
http://ir.canterbury.ac.nz/bitstream/10092/4085/1/thesis_fulltext.pdf
The first one is a documented proof and the second one is a third party's opinion. I can show you hundred proofs from the Chinese side if there's a need.