704
C H A S K O I
the idea of representing the earth’s surface on a cylinder, in which the length of the degrees of latitude were increased as they approached the pole in the same proportion as those of longitude decreased on the globe. This idea was perfected about 1590 by Edward Wright, an Englishman, and it is on his principle that the present charts are drawn on what is known as “ Mercator’s proMercator’s jection.” The advantage of this projection to projec . saiior js that the ship’s course between any two places is represented by a straight line. On a sphere the meridians all converge towards the pole, the degrees of latitude are equal, those of longitude decreasing towards the pole; on a Mercator’s chart the meridians are drawn as parallel lines, and the degrees of longitude are all equal. To compensate for this error, the degrees on the Mercator chart are increased as they approach the pole beyond their actual lengths, in the same proportion as the degrees of longitude on the sphere diminish in length as they approach the pole. The length of a degree of latitude in the parallel of 70° is consequently three times that of a degree at the equator. It is, however, only when equatorial and polar regions are contrasted that the distortion becomes evident—contiguous countries and seas appear but little out of proportion to each other, and no other projection is known that so well meets nautical requirements. Distances on a Mercator chart are measured on the latitude scale, on the sides of the chart, taking care to use that part of the scale which is in the same latitude as the ship; e.g., distances between places within the parallels of 50° and 60° must be measured upon the latitude scale between 50° and 60°. The British Admiralty charts are compiled, drawn, and issued by the Hydrographic Office. This department of the Admiralty was established under Earl Spencer Hydropy an or(Jer in council in 1795, and consists of
tke hydrographer, one assistant, and a draughtsman. The first hydrographer was Mr Alexander Dalrymple, a gentleman in the East India Company’s civil service. From this small beginning arose the important department which is now the main source of the supply of hydrographical information to the whole of the maritime world. The charts prepared by the officers and draughtsmen of the Hydrographic Office, and published by order of the lords commissioners of the Admiralty, are over 3100 in number. They are compiled chiefly from the labours of British naval officers employed in the surveying service; and also from valuable contributions received from time to time from officers of the royal navy and mercantile marine. In addition to the work of British sailors, the labours of other nations have been collected and utilized. Charts of the coasts of Europe have naturally been taken from the surveys made by the various nations, and in charts of other quarters of the world considerable assistance has been received from the labours of French, Spanish, Dutch, and American surveyors. The Admiralty charts are published with the view of meeting the wants of the sailor in all parts of the world. They may be classed under five heads, viz., ocean, general, and coast charts, harbour plans, and physical charts; for instance, the Indian Ocean, the Mediterranean, approaches to Plymouth, Plymouth Sound, and wind and current charts. The harbour plans and coast sheets are constructed on the simple principles of plane trigonometry by the surveying officers. (See Surveying, Nautical.') That important feature, the depth of the sea, is obtained by the ordinary sounding line or wire; all soundings are reduced to low water of ordinary spring tides. The times and Chaskoi, Chaskovo, Khaskoi, Haskoi, or Hasheights of the tides, with the direction and velocity of the tidal streams, are also ascertained. These MS. charts kovo, the chief town of a department in Bulgarian Eastern are forwarded to the Admiralty, and form the foundation Rumelia, 45 miles E.S.E. of Philippopolis. It has
o/Wce
C
of the hydrography of the world. The ocean and general charts are compiled and drawn at the Hydrographic Office, and as originals, existing charts, latest surveys and maps, have to be consulted, their compilation requires considerable experience and is a painstaking work, for the compiler has to decide what to omit, what to insert, and to arrange the necessary names in such a manner that while full information is given, the features of the coast are not interfered with. As a very slight error in the position of a light or buoy, dot, cross, or figure, might lead to grave disaster, every symbol on the Admiralty chart has been delineated with great care and consideration, and no pains are spared in the effort to lay before the public the labours of the nautical surveyors and explorers, not only of England, but of the maritime world; reducing their various styles into a comprehensive system furnishing the intelligent seaman with an intelligible guide, which common industry will soon enable him to appreciate and take full advantage of. As certain abbreviations are used in the charts, attention is called to the “ signs and abbreviations adopted in the charts published by the Admiralty.” Certain parts of the world are still unsurveyed, or not surveyed in sufficient detail for the requirements that steamships now demand. Charts of these localities are therefore drawn in a light hair-line and unfinished manner, so that the experienced seaman sees at a glance that less trust is to be reposed upon charts drawn in this manner. The charts given to the public are only correct up to the time of their actual publication. They have still to be kept up to date. B-ecent publications by foreign Governments, newly reported dangers, changes in character or position of lights and buoys, are as soon as practicable inserted on the charts and due notice given of such insertions in the Admiralty “Notices to Mariners.” During the year 1900, 102 new plates of charts and plans were engraved, 30 plates received the addition of 8 new plans, and 224 plates were largely improved by corrections and additions ; 4520 corrections were made to the plates by the engraver; 35,500 received minor corrections at the hands of the draughtsmen, and 875 “Notices to Mariners” were issued. The number of charts, printed for the requirements of the Royal Navy, and to meet the demand of the general public, during 1900, amounted to 580,207. These facts show the necessiiy of charts being closely watched by sailors and shipowners using them, to insure their being supplied with the most recently corrected charts. The dates of the corrections are noted at the foot of the charts—those of large corrections, and additions, for which the charts have been cancelled, being written in full against the imprint; while the date of smaller corrections, such as changes in lights and buoys, are noted in Roman numerals on the left-hand lower corner. For the mercantile marine the Board of Trade collects and publishes the above information in a small pamphlet, Notices to Mariners for Foreign-going Ships. This pamphlet, supplemented by a weekly issue, is supplied free of charge to the ships of the mercantile marine. The Admiralty charts, when issued from the London chart agent (J. D. Potter), have received all necessary corrections to date. Once out of his hands, there is no guarantee that further corrections are made before sale, by local firms at different ports ;■ and purchasers should obtain some assurance that they are correct to date. The charts are also supplemented by the Admiralty Pilots, or books of sailing directions, with tide tables, and lists of lighthouses, light vessels, &c., for the coasts to which a ship may be bound. The physical charts are the continuation of the work so ably begun by Maury of the United States and FitzRoy of the Royal Navy, and give the sailor a good general idea of the world’s ocean winds and currents at the different periods of the year; the probable tracks and seasons of the tropical revolving or cyclonic storms ; the coastal winds ; the extent or months of the rainy seasons ; localities and times where ice may be fallen in with; and, lastly, the direction and force of the stream and drift currents of the oceans. (t. A. H.)
