Page:The New International Encyclopædia 1st ed. v. 04.djvu/608

CHAKT. 528 CHARTE. giaplic Office of the United States Navy for the eunvenience of navigators who wisli to follow fjieat-circlo (■ourses; and the coast and harbor iharU of the United States, jjublished by the ■ Lnited States Coast and Geodetic Survey, are oil the polyeonic projection. Charts are con- structed « ith more accuracy than ordinary maps, and efforts are made to enil)od.v in them all the information possible. The meridians and paral- Icl.s of latituile are drawn at convenient intervals, and on liarl)or charts the e.xact geographical position of some datum point is given. One or more compass-roses (i.e. plans similar to the face of a compass-card) are engraved in the chart where most neeiled, or where thoy will not interfere with soundings or other matters, and these show the magnetic variation, while the annual change is recorded in a note. In the case of harbor charts the rise and fall of the tide and hnii-lidal interval are given: this is important when tin- tidal range is consideralde. for the depths, or soundings, recorded are based upon .some particular state of the tide, usually that of mean low water. Shoals and shallow waters are indicated by dotted shading, or stip- ()led tint, in order that their presence may more readily be noticed, and rocks are marked by crosses or other conventional signs. The sound- ings are expressed in fathoms, or in feet, which- evw will best serve in the particular locality. and a note under the title states which is used. The character of tiie bottom is indicated by symbols, giving the kind of material (sand, mud, rock) and its hardness, fineness, color, etc. Lighthouses, buoys, beacons, and other aids to navigation arc carefully shown in their proper position ; and, when desirable to do so, the proper courses for entering or leaving a port or channel are indicated l)y broken lines, alongside wbich the compass cours<'s are printed. The depths and coast-line in nearly all parts of the world are constantly changing, as are the light- houses, buoys, and aids to navigation. This requires unceasing watchfulness on the part of chart-issuing offices, and the correction of charts constitutes more than half the expense connected with their production and issue. Charts already printed and on the shelves of the issuing ofTice are corrected by hand, several draughtsmen being constantly engaged in the work. If, however, the correction in this manner takes more than a few minutes, the copies on the shelves are destroyed and a new edition jirinted with the correction embodied in the engraving. The sources of information for corrections are the reports from men-of-war or merchant ships, from lighthouse boards, inspectors of harbors, channels, and waterways, new surveys, and the like. These are embodied in Notices to Mariners and pub- lished at short intervals, usually once a week. The information i-; arranged in the most con- venient manner possilde for the use of naviga- tors, the ninnber of each chart alTeeted by a note being stated. In addition to this, the notices give a list of charts of which new editions have been published, or which have been extensively corrected. For pur|)oses of navigation the character of the projection (i.e. the plan by which the curved surface of the earth is represented on a plane) is most imjiortant. The Mereator projection is most user! and decidedly the most popidar. The meridians are rectilinear and parallel, and this enables the navigator to lay down the compass cour.se as a straight line; and charts on this l)rojection of the same scale and latitude may be joined at the edges. Neither of these importjint characteristics is possessed by the polyeonic, which is best suited to the delineation of snnill areas such as harbors of moderate extent or certain types of ocean charts. The line of sight and the great - circle course are nearly straight lines on a polyeonic chart, and areas and shapes near the central meridian are un- distorted. The saving of distance through fol- lowing great-circle areas is very slight except on long voyages, and the conditions of average wind and weather are likely to reduce the value of the saving even then, because the great-circle arc, when it differs from the rhumb line (q.v.), al- ways lies on the i)olar (and therefore usually the colder and stormier) side of it. Whether it is desirable to follow a great circle or not can readily be determined by comparing the course as laid down on a great-circle chart (gnonionic projection) with a wind, weather, and current chart, such as the pilot chart issued by the Hy- drographic Office of the United States Ka'y. See Pilot Chart. Charts are now chiefly printed from engraved plates (copi)er, e.xcejjt in France, where many soft steel plates are used), for various reasons, tiic |)rineipal of which is tluit it facilitates the introduction of new matter in certain jiarts with- out the necessity of reproducing the whole. To cU'ect the correction the plate is turned face downward on a smooth anvil or hard surface, and the area to be re-engraved smoothed ovit and the metal brought up flush with the general surface of the plate by beating on the back over the piedetermined area with a round-faced ham- mer. Preliminary charts, and others of tem- porary' interest, or of which the details do not change, are largely produced by iilioto-lithog- raphy. With this process tough, flexible jiaper cannot be satisfactorily used, and if a photo- lithographic chart is to be much handled it re- quires backing with cloth. As already stated, there are in the United States two chart-making otlices. the Hydrographic Office of the Xavy, and the Coast Survey, the latter publishing charts (about 800) of the United States coast only; and the former, charts (about l.")00) of the Great Lakes and of foreign territory and seas. The main ollicc of each of these establishments is in Washington, but for the i)urpose of gathering and disseminating in- formation of ser%-ice to navigators, the Hydro- graphic Office has braiiches in all the principal seaports of the United States and several on the Great L.akcs. It is likely that additional ones will soon be opened at Manila and Honolulu, with obsening stations at Guam and Tutuila, when these can be reached by telegraph. In Great Britain the Hydrographic Oflice is under the Admiralty. Charts arc also published by nearly all the European powers, and by Brazil, Chile, and Japan; and there are several private makers who issue charts of special localities. The price of Government charts is very low, barely sufficient to cover the cost of printing and pa pel"-. CHARTA, kjlr'ta. Ar.G.A. See Magna ClIAIilA. CHARTE, shiirt (Fr.. charter, from Lat. cliarta, paper). A French term, used especially