1882.Corea, the hermit nation. Dagelet can be visible from Corean peninsula.

Corea, the hermit nation. I. Ancient and mediaeval history. II. Political and social Corea. III. Modern and recent history (1882)

by Griffis, William Elliot, 1843-1928

（P110)
http://archive.org/stream/coreahermitnatio00grif#page/110/mode/2up/search/island
From a point on the sea-coast nearby, in fair weather, the island cone of Dagelet is visible.

（P206）
http://archive.org/stream/coreahermitnatio00grif#page/206/mode/2up/search/perouse
Deer are very plentiful, and the best hartshorn for the pharmacy of China comes from these parts. Out in the sea, abut a degree and a half from the coart, lies and island, called by the Japanese Matsushima, or Pine Island, by the Coreans U-lon-to, and by Europeans, Dagelet, This island was first discovered by the French navigator, La Perouse, in June, 1787. In honor of an astronomer, it was named Dagelet Island. "It is very sttep, but covered with fine trees from the sea-shore to the summit. A rampart of bare rock, nearly as perpendicular as a wall. completely surrounds it, except seven sandy little coves at which it is possible to land." The grand central peak towers four sousand feet into the clouds. Firs, sycamores, and juniper trees around. Sea-bears and seals live in the water, and the few poor Coreans who inhabit the island dry the flesh of the seals and large quantities of petrels and haliotis, or sea-ears, for the markets or the main land. The island is occationally visited by Japanese junks and foreign whaling ships, as whales are plentiful in the surrounding waters. The Japanse obtained the timber for the public and other building at their new setlement at Gansan from this island.

http://archive.org/stream/coreahermitnatio00grif#page/350/mode/2up/search/perouse
It was during the summer of this year, 1787, that La Perouse sailed along the eastern coast of Cho-sen, discovered the straits which bear his name, between yezo and Saghalin, demonstrated that the Gulf of Tartary divided Saghain from the Asian mainland, and that Corea was not sea-girt, and named Dagelet Island and its comparison Boussole. He had a copy of Hamel's book with him. He noticed that signal-fires along the coast, which from headland to headland, telegraphed to the capital the news of the stranger with his "black ship". Not as yet, however, as afterward, did the government connect the appernce of European vessels with the activity of the Christians within the realm, although La Perouse sailed under the flag which eveer afterward was indissolubly associated in Crean minds with Christianity