#Tides.# Information regarding tides is given on all large scale charts, and additional information and predictions may be found in the Tide Tables. On the charts of the United States coast there is a small tide table giving for the high and low waters the time relations to the moon's transit and the height relations to the plane of reference. On the British charts there is a brief statement as to the tides either at the port on the chart or in the general notes; this ordinarily gives the interval in hours and minutes between the moon's meridian passage and the time of high water for the periods of full and new moon, and also the amount in feet that the spring and neap tides rise above the plane of reference, and the range of the neap tide. The following is an example of such a tide note: "H. W. F. and C. Campbellton IV^h 0^m. Springs rise 10 feet, Neaps 7 feet." At some important ports information as to the state of the tide is given to vessels, either by means of signal balls, or by automatic tidal indicators, as at the Narrows in New York Harbor, where a large dial shows to passing vessels the height of the tide, and an arrow indicates whether it is rising or falling. The tidal information becomes important and must be considered in navigation or in anchoring in waters where the available depth at low water approximates the draft of the vessel. In the general use of coast charts it is also important to observe the effect of the stage of tide on the appearance of many features. Rocks rising some feet above low water may be entirely submerged at high water. In some areas the aspect may be radically changed between high and low water by the baring of extensive shoals or reefs. #Currents.# Information, when available, as to currents is given either by a note or by current arrows placed on the chart at the position of observation. Additional information as to certain regions is given in the United States Tide Tables. Tidal currents, flood and ebb, and currents not due to tidal action are distinguished by symbols, and the velocity is given in knots, and on some charts is indicated by the lengths of the arrows. Complete and systematic current observations have been made in comparatively few localities because of the time and expense necessary to get the full information as to the variations of the currents with the tides and seasons. Ordinarily therefore the current arrows shown on charts indicate only the average direction and velocity, or possibly only the conditions existing at the season when the survey was made. Oceanic and coast currents are probably much less uniform than might be inferred from the current streams drawn on maps and charts. A more systematic investigation of ocean currents is required to fulfill the needs of navigation.