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Proceedings of Royal Society of Edinburgh. [sess. 
a sailor a good guide for a fair passage through the Strait. As you 
see by Plate V. the temperature of the water, say, in the month 
of February at the Chinese coast is 11° C., while at the coast of 
Formosa it is 20°. If the captain will try during the month of 
February to follow the line of the temperature of 15° he will pass 
at a good distance from the dangers of both coasts. Plate YI I. 
shows the distribution of the specific gravity. At the Chinese 
coast in winter it is possible to find water at less than P0240 
while at the coast of Formosa it is seldom less than P0265. 
Every sailor knows how difficult the passage through the Strait 
of Formosa is. During the north-easterly monsoon the weather is 
very thick, and the depth of the sea cannot in these places be 
regarded as giving a good means for determining the position of 
the ship. It may happen that after a ship leaves say Nagasaki 
the captain never knows his position until he runs on the Chinese 
coast and wrecks his ship. My opinion is, that a regular tempera- 
ture service should be arranged from Turnabout Lighthouse ; every 
day a pilot boat should put to sea, taking temperatures both going 
out and returning, and the temperature of the water should be 
wired to all Chinese and Japanese ports for the information of the 
captains. By these means many ships would be saved from danger. 
The currents in the Straits of La Perouse are very complicated. 
Plate VIII. shows the distribution of the temperature of the surface 
water. There is a very narrow and long strip of cold water, which 
lies in the direction from N.W. to S.E. ; a vessel crossing that strip 
in July may have temperatures of 18° C., then 5°, and again 16° or 
1 8°. It would take me too long to explain the source from whence 
the cold water comes, and why it is constantly there ; it is the 
cause of fogs which render navigation in that place very difficult. 
I may briefly say that the Kuro-Siwo current partly enters the Sea 
of Japan, and the excess of water escapes partly through the 
Strait of La Perouse into the Okotsk Sea. Due to the rotation 
of the earth the current turns to the south-east and flows alongside 
the Island of Yezo. This water is warm and dense, having much 
salt in it. The water of the Okotsk Sea — particularly in the vicinity 
of the Island of Saghalien — is in summer also pretty warm, but it 
is much lighter than the water of the Kuro-Siwo, and thus while 
