Page:Popular Science Monthly Volume 8.djvu/538

 on which the chart has been constructed, and an explanation of the conventional signs used on it; these latter, however, are generally supposed to be known.

General notes regarding the winds, currents, tides, harbor facilities, etc., are frequently added, as also sometimes sailing-directions; but generally these are left for text-books, which, under the titles of "Directions," "Memoirs," "Manuals," or "Pilots," give to the navigator the information obtained by the hydrographer, with the general results arrived at, which cannot be engrossed on charts.

By a judicious arrangement and a complete index, these should be made as intelligible and as ready for reference as possible, and should contain all the points within the area treated on that are of interest to navigation.

The first treatise on marine surveying, published in a practical form, was by Alexander Dalrymple, in 1771. This was followed by the work of M. Beautemps Beaupré, in 1808; since which time there have been published many valuable works on marine surveying, adapted both to running surveys and to greater geodetical operations.

In hydrographic surveys and exploration, England has always been foremost. Her Hydrographic Office, dating from 1795, under Alexander Dalrymple, was not firmly established until 1828, when Captain Francis Beaufort became the hydrographer to the British Admiralty; since which time, under the administration of the line of distinguished navy officers his successors, it has steadily advanced, to the inestimable benefit of commerce, both British and foreign. At the present date the charts of this office number two thousand nine hundred and eighteen, and yet about one-half of the coasts and navigable waters of the world remain unsurveyed, a great part not even examined.

An interesting skeleton chart of the world, compiled at the British Hydrographic Office and attached to a paper delivered by Commander Hull, R. N., superintendent of the Admiralty charts, before the Royal United Service Institution, showed the portions of the coasts of the world surveyed, partially surveyed, and only explored. Taking this continent alone, between the parallels of 60° north and 60° south, beyond which whaling-vessels only generally go, it will be found by rough measurement that about 12,000 miles of the seacoast have been surveyed, 20,000 miles partially surveyed, and that 8,000 have been only explored. Coasts partially surveyed or only explored require the utmost caution for safe navigation; and, even with this, vessels are constantly in peril. For the remainder of the globe, with exception of Europe, the proportion of the inadequately-surveyed and almost unknown coasts and waters is much greater. This should demonstrate clearly the vast field of labor awaiting the maritime surveyor.

England perseveres in this work, and her hydrographic parties are found in every quarter of the globe, opening new channels to commerce, and defining the dangers of navigation. France, in her