HYDROGRAPHY. 319 



current, which, although interrupted at times by tidal action, 

 moves a large body of water through the canal from north 

 to south. Daring the winter, on the contrary, the winds blow- 

 ing violently from the south send the current in an opposite 

 direction, the mean level of the Red Sea attaining a height 

 of twelve inches over the Mediterranean. These currents 

 cause an annual movement of 400,000,000 cubic meters of 

 water from one sea to the other, and, with the tidal streams, 

 tend to counteract the effects of evaporation from Lake Tim- 

 sah and the Bitter Lakes, and to decrease the Amount of salt 

 in the latter. Between Port Said and Lake Timsah these 

 currents have a rate of from -^ to yu f a m ^ e an hour; but 

 between Suez and the Bitter Lakes they attain a rate of 1-^- 

 to 2 miles. The deposit of salt, 40 feet thick, at the bottom 

 of the Bitter Lakes, under these influences, aided by the pas- 

 sage of vessels, is being gradually diminished. 



An excellent survey of Mauritius and the surrounding 

 banks, on a scale of one inch to a mile, has been completed 

 by Lieutenant Coghlan, R.N. ; and Captain Wharton, R.N., 

 whose labors in the Red Sea were noticed in last year's Rec- 

 ord, has, during the past year, been engaged in a thorough 

 survey of the intricate coast and islands north and south of 

 Zanzibar, completing it from latitude 1 S. to 9 S., besides 

 surveying several harbors and approaches, and making a 

 series of deep-sea soundings for a projected telegraph cable 

 from Zanzibar to the Cape of Good Hope. 



In China, the coast between Hong-Kong and Foochow has 

 been carefully examined by Captain Napier, R.N., in H.M.S. 

 JVassau. This duty has included the survey of Hai-tan Strait 

 with the approaches, and the execution of several plans of 

 harbors and anchorages. 



The officers of H.M.S. Sylvia have been engaged in an ex- 

 amination of the ship-channels between the islands off the 

 southwestern part of Korea, lying directly between Japan 

 and the northern ports of China, and making surveys on the 

 coasts of Nipon and Kiusiu. 



In the Fiji Islands, steady progress has been made in their 

 survey by Lieutenant Moore, R.N. ; the whole of the coast 

 ofVitiLevu, with its off-lying islets and reefs, and Kandavu 

 passage, the main approach to the harbor of Savu, the new 

 capital, being now completed. 



