OCEAN SURVEYING. [From the Times, January 31.]

New Zealand Spectator and Cook's Strait Guardian, Volume IX, Issue 822, 18 June 1853, Page 4

OCEAN SURVEYING. [From the Times, January 31.]

"With our late advices from the Cape of pood Hope we have received intelligence of an interesting nature from the expedition which left England m tbespiing of the past, year, for the purpose of making a lengthened survey of the __Jj£cific_and_conducting the^ various scientific operations connected therewith. The vessels selected for this important service were the Herald and Toreh — the latter a steamer of small draught of water, and both under the command of Captain Henry Mangles Denhara, R.N., F.R. S., an officer well kuown for his scientific attainments, and possessing, in an eminent degree, all the qualifications requisite for the superintendence of an unde; taking of such vast importance. Our information bears the date of December 9cb, 1852, at which period the Herald and her steam tender were -at Simon's Bay, Cape of Good Hope, making active preparations for proceeding further on their voyage of discovery. We select those portions of the letter-before us which possess the gieatest interest : — " The satisfactory results which have attended our passage thus ftr, long as it has been, have not only obtained for us commendation, but also elicited a wish at head-quarters that our voyage should, include the Cape of Good Hope. Such a detour, however, unavoidably protracts it still more. The fact of our having ieceived instructions to obtain deep sea soundings at rapid intervals of time necessarily checked our progress almost every hour, and was the means of the discovery of two ocean banks of coralline structure, extending some 80 miles separately, and suddenly jumping from 200 fathoms, with no bottom, to 19 fathoms at a cast of the lead. We had determined that our magnetic observations should form a close link chain throughout each successive 24 hours. To fulfil this intention, j our run between sunset and sunrise, however fair the wind might be, could not be more than 40 miles. "In order to test the magnetic deviation of both vessels, at every anchorage they had to ie swung, and the meridian distances, astronomically, of one place with another bad to be determined. According to the tranquillity of the sea, our soundings were carried to the depth of 1,000 and 1,500 fathoms, the temperature at that depth being found to have decreased to 40 deg., though 90 deg. at the .surface. But the depth of water however great the temperature at the was never lower than 40 deg. - By lowering, down a white plate in a pitch kettle the sun's rays were traced to have penetrated the ocean 66 fathoms. At last our soundings extended to the unprecedented cast of 8f miles depth, and oar thermometer here brought up results from greater depths than were ever previously obtained. The great depth of 15,412 yards was obtained at a position about midway between Tristan d'Acunba and Cape Horn. We visited the island of Tristan 20 years ago, since which time no ship has touched there. On this occasion we bad to correct the longitude many miles, .and to prove that the magnetic variation was double that recorded. A survey of this island, and fixing the relative positions of the others called Nightingale and Inaccessible, occupied some time. Here we found 81 British Protestants isolated — a most interesting incident. We furnished them with gunpowder to blast ■tone,, and tools to* work with for a church and schoolroom, and replenished their books and necessaries. ••To effect the survey of the banks (one of which we have named Victoria) required many . eyolutionjs. The Herald was at anchor in the middle of, the ocean at intervals during more than three weeks, to ■ the utter astonishment of some ships whose tracks lav iv the direction of

our position. We were necessarily subject to the vicissitudes of a raid-ocean anchorage, but we have not lost an anchor, spar, or sail, nor a man overboard during our peregrination thus far through a route of 10,000 roilei. We have experienced a variety of phenomena of a most interesting nature, varied scenes and climate. A fourth series of work is preparing for despatch by the packet of the 20th instant. Our refit, taking in provisions, &c, will be completed in a day ot two, when we start for Sydney, expecting to eat our Christmas dinner near to the island of St. Paul and Amsterdam. The officers and crew perform their duties most cheerfully, and to the entire satisfaction of the commander of the expedition. When we arrive at the actual region of our survey we shall all be in excellent training."