1897.Korea and Her Neighbours by Isabella Lucy Bird

Korea and Her Neighbors: A Narrative of Travel, with an Account of the Recent Vicissitudes and ... (1897)
Author: Isabella Lucy Bird
Publisher: Revell
Year: 1897
http://www.archive.org/details/koreaandherneig02birdgoog


Text: Sea of Japan
http://www.archive.org/stream/koreaandherneig02birdgoog#page/n100/mode/1up/search/japan

The Han itself, rising in the Diamond Mountain of Kong-won-Do, and formed by a number of nearly paralellaffuents, next to the border river Am-nok, is the river of Korea, which it cuts nearly across, its eastern extremity being within 25 miles of the Sea of Japan and its western at Chemulpo. I ascended it to within 40 miles of the Sea of Japan, and estimate the length of its navigable waters for small flat-bottomed craft at about 170 miles.

Attached map; unconfirmed (data defect)
http://www.archive.org/stream/koreaandherneig02birdgoog#page/n90/mode/1up

There are some descriptions of "east coast (of Korea)", although there are no "East Sea" and there are the name of Sea of Japan on the text.
http://www.archive.org/stream/koreaandherneig02birdgoog#page/n29/mode/1up/search/east
Owing to the configuration of the peninsula there are few good harbors, but those which exist are open all the winter. The finest are Fusan and Won-san, on Broughton Bay/ Chemulpo, which, as the port of Seoul, takes the first place, can hardly be called a harbor at all, the "outer harbor," where large vessels and ships of war Lie, being nothing better than a roadstead, and the "nner harbor," close to the wtown, in the fierce tideway of the esturary of the Han, is only available for fve or six vessels of small tonnage at time .The east coast is steep and rocky, the water is deep, and the tide rises and falls from 1 to 2 feet only. On the southwest and west coasts the tide rises and falls from 26 to 38 feet!


I can confirm "Sea of Japan" on attached map of Korea and her neighbor on 1898 eddition
Korea and her neighbors; a narrative of travel, with an account of the recent vicissitudes and present position of the country (1898)
Author: Bird, Isabella L. (Isabella Lucy), 1831-1904
Subject: Korea -- Description and travel
Publisher: New York, Chicago [etc.] F.H. Revell Co.
http://www.archive.org/details/koreaherneighbor00bird
Attached map;
Sea of japan: Sea of Japan
Broughton bay: Broughton bay
Strait of Korea: Strait of Korea
http://www.archive.org/stream/koreaherneighbor00bird#page/n20/mode/1up