Page:Popular Science Monthly Volume 8.djvu/532

514 the islands shown on the present charts with queries, in regions not yet sufficiently explored, will prove to have been similarly misplaced at that early date.

The science of hydrography, by which the correct establishment of positions and exact delineations of the shores are attained, remained meagre until the middle of the eighteenth century, when it may be said to have fairly commenced with the expeditions of Captain James Cook under the auspices of Great Britain, which were soon followed by similar undertakings by other nations, especially by France and Russia, and at a later period by the United States. Almost all these voyages of discovery and explorations were of circumnavigation, and, though many localities were examined more or less in detail, in general they could only result in skeleton charts to be filled in by systematic surveys, at a future period, conducted under the direction of organized institutions. In the first quarter of the present century hydrographic offices were established by the principal maritime nations for the survey of their waters at home and in their colonies. To the hydrographic office of Great Britain, which has been liberally provided with means by the Government, belongs the credit of having taken the lead in extending systematic surveys into almost every water traversed by vessels, and to its zeal and energy all navigators and commercial communities will ever be deeply indebted. At present almost every nation having a seaboard has it hydrographic office for the survey of its own coast, and to participate in the survey of such waters as are considered the common possession of nations, and of the coasts of countries which do not provide for surveys. Almost every European nation has provided for the trigonometrical survey of its entire domain.

The British Ordnance Survey, commenced in 1783, will probably take ten years yet to complete; the trigonometrical surveys of France, Germany, the Netherlands, Belgium, and the European portion of Russia, are in course of completion; in other countries they are in progress. The several governments have also agreed on measures for the careful connection of the triangulations across the borders of their states. Where such rigid geodetic operations were instituted previous to the hydrographic survey of the coasts and waters, they furnish the hydrographic surveyor, not only with the correct outlines of the coast, but also with the precise position of the landmarks upon which he may base his work, or, in other words, a skeleton for the same. But, when such surveys are not existing, he is compelled to lay down the coast-line also, with its detail as far inland as there are landmarks auxiliary to navigation, thus performing the labors of the topographer as well as those of the hydrographer. Both require the greatest care, for on the precise establishment of the landmarks depend in a great measure the delineation of the shoreline, the establishment of outlying dangers, and the exact location of