Page:Journal of the Royal Geographical Society of London, Volume 1 (2nd edition).djvu/239

Rh In both oceans there appears to be, on the whole, a north-easterly current between the trade winds. In the Atlantic it was found to average thirteen miles a day; and in the Pacific, twenty-three miles a day. In the vicinity of the Gallapagos, however, there is an exception to this remark, as the current there appears always to run to the westward, and with considerable rapidity.

The rates of the currents in both oceans are materially different in different meridians: those in the Atlantic increasing with westerly longitudes, and those in the Pacific, on the contrary, decreasing—the former attaining its maximum near the Gulf of Mexico, the latter near the Gallapagos. They are also affected by the westerly monsoons.

Questions connected with the saltness of the ocean, which may be obtained by its specific gravity, are also of much hydrographical interest. It has been supposed, that, with the exception of certain gulfs, into which large fresh-water rivers emptied themselves, the saltness of the ocean diminishes towards the poles; but the experiments of Bladh, reduced by Kirwan to the temperature of 16°, do not justify this opinion, which is further not supported by the researches of De Humboldt. Captain Beechey has appended a table of experiments to his narrative, in which the specific gravity of the surface of the sea, reduced to the temperature of 60°, and corrected for the error of the hydrometer, is given for every second degree of latitude. From these tables, it would appear that the specific gravity is at its maximum between the tropics,—that it increases to about 40° N. lat.,—and then again diminishes. In the South Atlantic, the specific gravity of the sea-water was also found to be less in the highest latitudes; and the same results were obtained from the observations of 1825 and 1828. In the Pacific Ocean, where the experiments ranged from the equator to 71° N. latitude, and from the equator to 88° S. latitude, the results are still more striking; and accord remarkably with those obtained by Drs. Marcett and Traill, and Captains Scoresby and Ross. No experiments are recorded on the comparative saltness of the surface and the deep water.

—The meteorological researches are confined to observations on the aurora borealis, and on the pressure, temperature, and humidity of the atmosphere. The expedition had frequent opportunities of observing the aurora borealis in the autumns of 1826 and of 1827. From the 25th of August, on which day it is remarkable that in both years it made its first appearance, until the 9th of October, about the time of the departure of the Blossom from the northern regions, in both years this beautiful meteor was visible every night that was clear, or when the clouds were thin and elevated: it never appeared in wet weather. In 1826, when the weather was settled,