harbor improvements and various engineering works, for defensive works and other military uses, for the fishing interests, and for general information as to the coastal regions. Charts will furnish much of interest and instruction to the traveler by sea and the dweller near the coast, who will learn to read them. Passenger steamers should more often for the interest of their patrons display charts of the waters traversed. No written or verbal description can give as clear an idea of geographical features and relations as a good map or chart.

As the charts are revised from time to time, a comparison of editions at different dates furnishes a record of the changes wrought by nature or man, and this is especially useful in studying the action in many harbor and river entrances, as well as for historical purposes.

Requirements for charts. As charts are maps of the water areas, including the adjoining land, and intended primarily for the use of mariners, they differ in important respects from topographic maps or general maps, even such as include the water areas. The main requirements for charts are these; correct and complete information, early publication of new data, clear and intelligible representation of the information, convenient arrangement as navigational instruments, and high standard of publication.

The special and sometimes difficult conditions under which charts must be used on shipboard call for good judgment throughout their preparation. Even the paper on which they are printed is of importance, in order that they may be sufficiently durable and suitable for plotting.

Information given on charts. It is evident that it is impossible to represent on a chart of any practicable scale all the features that exist on the corresponding area of the earth's surface. It is essential, therefore, that a selection be made of the classes of facts that are to be shown, as well as of the detail that is to be used for each class. The practical utility of the chart depends largely on the good judgment used in this selection. In the information shown, charts differ from maps principally in representing by soundings and curves the configuration of the bottom of the water area, and in showing ordinarily the topographic features only in the vicinity of the coast line.

The convenience of mariners should govern in the selection and arrangement of the information to be shown on charts, though they may be made useful for other purposes so long as this convenience is not lessened. The needs and preferences of navigators alone, however, differ so much that a reasonable chart must be somewhat of a compromise between conflicting views. For certain classes of navigation a boldly drawn chart showing only the dangers and a few other soundings and some landmarks might be useful. For other maritime purposes a more detailed chart would be valuable. The first, however, would fail to give facts often demanded in the navigational use of the chart, and the second if carried to an extreme would make a chart difficult to use.