Chapter III: Preface (3)

#Plane of reference.# The soundings given on the chart express the depth of water when the tide is at the height adopted for the plane of reference; this same plane is used in the tide tables, which thus will indicate the amount to be added to the soundings when the tide is above the plane, or to be subtracted when it is below. In order to be on the safe side the plane of reference adopted is always some low stage of the tide, so that there is usually more water than shown on the chart.

On the British and German charts the soundings are reduced to the mean low water of ordinary spring tides, unless otherwise stated. On the charts of the Coast and Geodetic Survey the following are the planes of reference: for the Atlantic and Gulf coasts, the mean of the low waters; for the Pacific coast, Alaska, and the Philippines, the mean of the lower low waters, except for Puget Sound and Wrangell Narrows, where planes two and three feet lower respectively have been adopted. According to the Tide Tables for 1908, at New York (Sandy Hook) the tide will fall below the plane of reference on 135 days during the year, but the extreme low tide will be only one foot below the plane. At Portland, Maine, in 1908, the extreme low water is 2.1 feet below the plane, and at San Francisco 1.5 feet. Of course when the tide is below the plane of reference the amount must be subtracted from the depths shown on the chart.

Strong winds and unusual barometric pressure may have a marked effect on the height of tide, so that it may differ appreciably from the predicted height, which is of course based on normal conditions. At Baltimore and at Willets Point observation shows that a heavy wind may reduce the tide four feet below the predicted heights.

#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.

The tidal currents seldom turn with the tides, and there may be an interval of as much as three hours between the time of high tide or low tide and slack water. This leads to the apparent anomaly that in cases the current may be running with its greatest velocity at the time of high or low water, and may be running into a channel for several hours after the tide commences to fall. It is therefore, evidently, not safe to draw inferences as to currents solely from the tidal heights.

There are passages where the tidal currents become of the greatest importance to navigation, as, for instance, in Seymour Narrows on the inside route to Alaska, where the current velocity reaches 12 knots and the interval of apparent slack water lasts but a few minutes.

#Elevations.# The unit used for elevations is also stated on the face of the chart, as also the plane to which elevations are referred. On the United States charts this is generally mean high water and on British charts the high water of ordinary spring tides. Rocks and islets usually have figures shown beside them, either in brackets or underscored, which indicate the height above high water. Rocks which are bare at low water sometimes have a note "dries" or "bares" so many feet, indicating their height above low tide, although they are covered at high tide. The British charts in some regions where there is a large range of tide have underlined figures in the area between high water and low water indicating the heights above low water, or the depths of water over the bank at high water, as explained in each case.

#Topography.# The land area on most charts is distinguished from the water area by a stipple or tint; on some charts the topographic features have, however, been depended upon to bring out the land from the water. The solid shore line is the high-water line, and should be clear on the chart; the area between high and low water is sanded or otherwise shaded on all charts. The relief of the land is represented by hill shading or by contour lines which are the successive curves of elevation on the land. Topographic symbols are used for some of the more important features, such as cliffs, rocky ledges, buildings, bridges, trees, roads, etc. It is important for the navigator to understand the significance of the hill representation and the symbols, as they will aid him in recognizing a coast or island, and in identifying landmarks.

#Date of survey and publication.# There is usually an authority note on each chart showing the source of information or date of survey; if on a coast subject to change, the latter is important. On the United States Coast Survey charts the date of publication of the edition is given, and on British and other charts the date of both large and small corrections. The chart catalogues give the dates of the last editions, or the dates of extensive corrections, and this affords a means of seeing whether the copy of the chart in use is the latest edition available.

USE OF CHARTS IN NAVIGATION.

#Chart working.# In crossing the open and deep portions of the ocean, where the only data given may be the projection lines and soundings far deeper than can be reached with navigational sounding machines, the chart is used to lay out in advance the general course to be followed and to plot the positions of the vessel at intervals either as determined by observations or, lacking these, by dead reckoning. When necessary the courses of the vessel are modified as the plotted positions are found to fall one side or the other of the proposed general track.

The principal operations on a chart are plotting or taking off positions by latitude and longitude, laying down or taking off bearings, directions, and courses, plotting or measuring distances, and laying down or taking off angles.

To plot a position by its latitude and longitude on a mercator chart, set a parallel ruler on the adjacent parallel and then move it to the required latitude as shown by the border scale at either side; then with a pair of dividers at the upper or lower longitude border scale take the distance from the nearest meridian and lay this distance off along the edge of the parallel ruler. The latitude and longitude of a point are taken from the chart by reversing this process, or with the dividers only. A direction is laid down on the chart or read from the chart preferably by using some form of protractor and measuring the angle from the projection lines. In this country it is more commonly done by carrying the direction with a parallel ruler either from or to a compass rose printed on the chart. Distances are measured or laid down on a mercator chart by using the latitude border scale for the middle latitude. On polyconic and other larger scale charts distances are measured from the scales printed on the chart. It should be remarked that in general where special accuracy is required distances should be computed and not scaled from any chart, because of the error due to the distortion of paper in printing.

The use of protractors on charts in plotting by angles in the three-point problem will be referred to later.

The course to be steered to allow for a set due to current or wind may be obtained by a graphical solution on the chart, though it will be preferable to do this on other paper, using a larger scale. (Fig. 38.) The direction and velocity of the set and the course and speed of the ship may be considered as two sides of a parallelogram of forces, of which the diagonal is the distance and course made good. To obtain the course to steer to reach a given point with a given current and speed of vessel, lay down the direction of the destination; from the starting point lay off the direction of set and the amount in one hour; from the extremity of this describe an arc with radius equal to the speed of the vessel in one hour. A line drawn from the extremity of the direction of set to the point of intersection of the arc and the course to be made good will give the direction of the course to be steered, and the point of intersection will also be the estimated position of the vessel at the end of the hour's run.

#Methods of locating a vessel.# The principal methods used for locating the position of a vessel are by astronomical observations, by dead reckoning, by compass bearings, by ranges, by horizontal angles, by soundings, by vertical angles, and by sound. The full discussion of these methods pertains to navigation and pilotage, and they will be only briefly referred to here as to their graphical application to charts.

#Astronomical methods.# There are a number of methods of obtaining the position of a vessel by astronomical observations. When the position is computed the chart enters into these only in the plotting of the final result, so that with one exception these methods will not be referred to further here.

The elegant method discovered by an American seaman, Captain Sumner, in 1843, is in part graphical, to be worked out upon the chart. This method is based on the obvious fact that at any instant there is a point on the earth having the sun in its zenith and which is the center of circles on the earth's surface along the circumference of any one of which the sun's altitude is the same at all points. A short portion of such a circle may be considered as a straight line and can be determined by locating one point and its direction, or two points in it. This is known as a Sumner line. (Fig. 39.)

From an observation of the sun's altitude and azimuth and an assumed latitude a position is computed and plotted and a line drawn on the chart through this position at right angles to the azimuth of the sun as taken from the azimuth tables and laid off from a meridian. Another method is to compute positions with two assumed latitudes and plot the two resulting positions and draw a line through them. The vessel must be somewhere on the resulting Sumner line. A good determination may be obtained by the intersection of two Sumner lines obtained from two observations of the sun with sufficient interval so that there will be a change of azimuth of as much as 30 degrees to give a fair intersection. Allowance must be made for the movement of the vessel between the two observations by drawing a line parallel to the first and at a distance equal to the distance made good. An excellent intersection may be obtained by observation of the sun, and before or after it of a star in the twilight at a different azimuth.

FIG. 38.]

FIG. 39.]

FIG. 40.]

Even a single Sumner line, however, furnishes valuable information, as it may be combined with other sources of information to obtain an approximation to the position. The vessel must be somewhere on this line, and this gives a good check on the position by dead reckoning, or an intersection may be obtained with a line or bearing of a distant land object, or a line of soundings may be compared on the chart with the Sumner line.

If an observation is taken when the observed heavenly body is bearing abeam, it is evident that the resulting Sumner line will be the direction of the course of the vessel, and this fact may be useful in shaping the course when nearing the land or a danger.

#Dead reckoning.# When impossible to obtain the position by any other means, it is computed or plotted from the last determined position, using the courses and distances run as shown by compass and log and allowing for effect of current and wind. Because of uncertainties in all these elements, positions so obtained may be from five to twenty miles in error in a two-hundred-mile run, depending of course to some extent on the speed of the vessel.

#Compass bearings.# A compass bearing of a single object, as a lighthouse or a tangent to a point of land, laid down on the chart, shows that the vessel is somewhere on that line, and when combined with other information, as with a Sumner line or the course by dead reckoning or the distance by a vertical angle, will give a position whose correctness of course depends on the accuracy of the data used. Bearings of two objects not in the same direction give two lines on the chart whose intersection is the position. This will be very weak if the angle of intersection is acute, and will become stronger as it approaches a right angle. A bearing of a third object should be taken when practicable, as it affords a valuable check in that the three lines should intersect in the same point; if they do not do so when plotted the error is either in the observations, or the compass, or the plotting, or the chart. (Fig. 40). All compass bearings are of course dependent upon the accuracy of the compass and the knowledge of its errors due to the local magnetic effect of the ship, and also upon the correctness with which the magnetic variation from true north is known. Bearings of near objects should therefore always be preferred, and those of distant objects considered as giving only approximate positions. An error of one degree in the bearing of an object 30 miles away will deflect the plotted line about one-half mile. Because of the facility with which they may be taken compass bearings are much used for inshore navigation, but in point of reliability they are inferior to some of the other methods.

A single or "danger" bearing of an object is often a valuable guide in avoiding a danger. For example, a reef may lie to the westward of a line drawn South 10° East from a lighthouse; in approaching a vessel will pass safely to the eastward of the reef if the lighthouse is not allowed to bear any to the northward of North 10° West. (Fig. 41.)

Two successive bearings of a single object, as, for instance, a lighthouse, noting the distance run in the interval, afford a convenient and much used means of locating the position with respect to that object. Such bearings are drawn on the chart in reversed direction from the object. The distance run between the bearings, as read by the log and corrected for current if practicable, is scaled off with dividers and the course of the vessel is set off with parallel ruler; the latter is then moved across the two plotted directions until the distance intercepted between them equals that scaled with the dividers, and the edge of the ruler then represents the track of the vessel. (Fig. 42.) If the angle from the bow, or from the course of the vessel, for the second bearing is double that for the first bearing, the distance from the object at the second bearing is equal to that run by the vessel in the interval, and the use of this simple relation is designated as "doubling the angle on the bow." If the angles between the course and the object are respectively 45° and 90° when the two bearings are taken on an object on the shore, the distance that the ship passes offshore when the object is abeam is equal to the distance run between the two bearings; this is a much used navigational device, known as the "bow and beam bearing" or the "four-point bearing." There is an advantage, however, in using bearings at two and four points (or 22.5° and 45°), as these give the probable distance that the object will be passed before it is abeam.

#Ranges.# A valuable line of position is obtained by noting when two well-situated objects are in range, that is, one back of the other in the line of sight from the vessel, as, for instance, a church spire appearing behind a lighthouse or a rock in line with a prominent point. Such ranges are of course entirely free from compass errors, and should be noted whenever there is favorable opportunity. The value of the range in plotting will increase with the distance between the objects, and if the two are close in proportion to the distance to the vessel the direction will be weak owing to the uncertainty in drawing a direction through close points. Artificial ranges are often erected as aids to navigation, usually to indicate the course to be followed in passing through a channel. Ranges afford a valuable guide in avoiding dangers, as for example an inspection of the chart may show that if a certain lighthouse is kept in line with or open from an islet a dangerous shoal will be given a good berth; on coasts not well buoyed such danger ranges are sometimes marked on the charts. (Fig. 43.)

FIG. 41.]

FIG. 42.]

FIG. 43.]

#Horizontal sextant angles.# The location of a position by the three-point problem, using sextant angles, is much more exact than by bearings, but is less used because not so well known and also because additional instruments are required and the conditions are not always favorable. It is so valuable a method, however, that it should be used, when necessary, on every well-equipped vessel. A single horizontal angle taken with a sextant between objects, as two lighthouses, defines the position of the vessel as somewhere on the circumference of a circle passing through the two objects and the vessel. A protractor laid on the chart with two of its arms set at the observed angle and passing through the two objects, will permit of locating two or more points of this circle on the chart. This furnishes a line of position which may be combined with other information to locate the vessel. With a compass bearing of one of the objects the position may be plotted directly from the single angle. Two sextant angles measured at the same instant between three objects furnish one of the most accurate means of locating the position of a vessel, this being the same method that is ordinarily used in hydrographic surveying, known as the three-point problem. (Fig. 44.) The two angles are conveniently set off on a three-arm protractor, which is shifted on the chart until the three arms touch the three points, when the position of the center is plotted. A third angle to a fourth point furnishes a valuable check in case of doubt. Two angles may also be taken to four objects without any common point, and in this case portions of the two circles of position are plotted and their intersection will be the ship's position.

The value of this method depends largely on the selection of favorably located objects, and it is quite important that the principles of the three-point problem be understood. If the ship is on or near the circumference of a circle which passes through the three objects the position will be very weak, and the same is true if the distance between any two of the objects is small as compared with the distance from them to the vessel. A useful general rule is that the position will be strong if the middle one of the three objects is the nearest to the vessel, provided that no two of the objects are close together in comparison with the distance to the vessel.

A single sextant angle furnishes a means of avoiding a known danger by using what is known as the horizontal "danger angle." (Fig. 45.) Note two well-defined objects on the coast either side of the danger to be avoided and describe a circle through them and passing sufficiently outside of the reef to give it a safe berth. With a protractor on the chart note the angle between the objects at any point on the outer part of this circle. If in passing, the angle at the ship between the two objects is not allowed to become greater than this "danger angle" the danger will be given a sufficient berth. This method as well as any use of sextant angles or bearings depends of course on the accuracy of the chart, and caution must be used where it is not certain that the chart depends upon an accurate survey.

FIG. 44.]

FIG. 45.]

FIG. 46.]

#Soundings.# Even if objects cannot be seen, due to distance or thick weather, the chart furnishes a valuable aid when a vessel has approached within the limits where it is practicable to obtain soundings. Modern navigational sounding machines permit of obtaining soundings to depths of nearly one hundred fathoms without stopping the vessel. A rough check is at once obtained by comparing such soundings with those given on the chart for the position carried forward by dead reckoning. If a number of soundings are taken and plotted on a piece of tracing paper, spaced by the log readings to the scale of the chart, and this tracing paper is laid over the chart and shifted in the vicinity of the probable position until the soundings best agree with those on the chart, a valuable verification of position may be obtained. This is particularly the case if the area has been well surveyed, and the soundings taken on the vessel are accurate, and the configuration of the bottom has marked characteristics. For instance, in approaching New York the crossing of the 30, 20, and 10 fathom curves will give a fair warning of the distance off the Long Island and New Jersey coasts, and soundings across such a feature as the submerged Hudson gorge extending to the southeastward of Sandy Hook will give a valuable indication of position. The taking of soundings should be resorted to even in favorable conditions, in approaching shoal water, as a check on other means of locating the vessel. Many marine disasters are attributed to failure to make sufficient use of the lead, the simplest of navigational aids.

#Vertical angles.# The vertical angle of elevation of an object whose height is known will give the distance, and combined with a bearing or other information this permits of locating a vessel where better means cannot be used. Distance tables are published for this method. (Fig. 46.) The vertical angle is measured with a sextant and must be the angle at the ship between the top of the object and the sea level vertically beneath it; for a hill or mountain, therefore, the eye of the observer should be near the water. The object should not be so distant that curvature becomes appreciable. The "vertical danger angle" is a means of avoiding a known danger, on a principle similar to that of the horizontal danger angle; that is, the angle of elevation of a known object is not permitted to become greater than a fixed amount depending on the distance from the object to the danger to be avoided.

#Positions by sound.# In thick weather sound affords a valuable aid to the navigator. In narrow passages noting the echo of the whistle from a cliff is a method resorted to, as for instance in Puget Sound and along the Alaska coast. Fog whistles and bell buoys are maintained at many places. Submarine bells have recently been introduced at a number of points along the Atlantic coast, and vessels may be equipped to receive these submarine signals transmitted through the water, which indicate also the general direction from which the sound comes.

#Need of vigilance.# Too great importance cannot be attached to frequent verification of positions by the best available means, particularly when approaching the land. Neglect of this or overconfidence has caused many disasters. A notable instance was the loss of one of the largest Pacific steamers on the coast of Japan in March, 1907. In the afternoon of a clear day this vessel ran on to a well-known reef about a mile from a lighthouse, resulting in the total loss of vessel and cargo valued at three and a half million dollars. The captain was so confident of his position and that he was giving the reef a sufficient berth that he laid down no bearings on the chart and took no soundings.

#Instruments.# The principal instruments needed for use with charts are; dividers for taking off distances and latitudes and longitudes, parallel ruler for transferring directions to or from a compass rose and for taking off or plotting the latitude on a mercator chart, protractor of 180 degrees for reading the angle with the meridian of any direction or for laying off on the chart any given angle with the meridian, and three-arm or other full-circle protractor for plotting a position by the three-point problem.

Parallel rulers on the principle of Field's are strongly recommended for chart work, as they combine in a single instrument the advantages of a parallel ruler and a 180-degree protractor. Any direction can be read or laid off by simply moving the parallel ruler to the nearest projection line, which is a process not only more convenient than referring to the compass rose printed on the chart but also more accurate because of the longer radius. These instruments can also be used the same as a plain parallel ruler. Field's parallel rulers are made in two forms, one rolling and the other sliding. The former is a single ruler with edge graduated 90 degrees either way, and mounted on rollers; it is the most rapid instrument for reading or laying off a direction, but it requires a smooth surface. The latter is an ordinary two-bar parallel ruler with edge when closed graduated 90 degrees either way; it is a very serviceable instrument and probably more to be depended upon for ordinary use than the rolling form. Some form of combined protractor and parallel ruler should be in every navigational equipment, and it is unfortunate that these instruments are not better known in this country. There are other forms of half-circle protractors which are used on the same principle, that is, of bringing the center on to a projection line and reading where the line cuts the border graduation of the protractor. Thus a semicircular protractor is used with a separate straight edge, along which it is slid to the nearest meridian; another form is the simple circular protractor with a thread fastened at the center. All these forms of protractors, it will be noted, are intended to work from the true meridian, and they are usually graduated in degrees only; the use of degrees instead of points is becoming much more general in navigational work, and reference to the true meridian is also more common than formerly.

The standard three-arm protractor, or station pointer, as it is known to the English, should be a part of every navigational outfit because of its value in locating a position by the three-point problem. A recent American invention, Court's three-arm protractor, is an instrument made of celluloid for the same purpose. It should not be considered as a substitute for the standard metal instrument, but it is a simple, cheap, and handy supplement to it, as it may be readily used for small angles and short distances where there are mechanical difficulties in working with the metal three-arm protractor. Other protractors can be used for the three-point problem, as, for instance, Cust's protractor on celluloid, on which the angles are drawn in pencil and erased, and the tracing-paper protractor.

#Degree of reliance on charts.# The value of a chart must not be judged alone from its general appearance, as skill in preparation and publication may give a handsome appearance to an incomplete survey. On the other hand a thorough survey might through poor preparation result in a chart defective either in information or in utility.

The degree of completeness of the soundings, the character of the region, and the date of the survey should be taken into account in deciding as to the amount of reliance to be placed on the chart. Areas where the soundings are not distributed with fair uniformity may be assumed not to have been completely surveyed. Caution should be used in navigating on charts where the survey is not complete, and even where careful surveys exist care must be taken if the bottom is of very irregular nature with lumps near the navigable depth, as for instance on some of the coral reef coasts. Isolated soundings shoaler than the surrounding depths should be avoided, as there may be less water than shown. In such a region, unless the whole area is dragged, it is impossible to make it entirely certain that all obstructions are charted.

While an immense amount of faithful work has been put into the preparation of many charts, the user must constantly exercise his own judgment as to the reliance to be placed on them. A coast is not to be considered as clear unless it is shown to be; buoys may get adrift and be in a different position or be gone altogether; fog signals vary in distinctness owing to atmospheric conditions; extreme or unusual tides may fall below the plane of reference; owing to strong winds the actual tide may differ from the predicted tide. Errors sometimes creep in from various sources, such as those due to different reference longitudes or the use of a corrected longitude for a portion of the chart without changing other positions to which the same correction is applicable; clerical and printing errors may occur; there are sometimes omissions in surveys; a feature may get plotted in two different positions; tide rips are reported as breakers and floating objects as rocks or islands, and thus many dangers have gotten on the charts which cannot be found again, and false reports are sometimes made to shield some one from blame. Most of these classes of errors and uncertainties, however, disappear in the use of charts of a thoroughly surveyed coast.

#Use the latest editions of charts.# The latest edition of a chart should always be used and should be corrected for all notices since its issue. Carelessness or false economy in not providing the largest scale or the latest chart has been the cause of more than one marine disaster.

The British Board of Trade issue the following official notice to shipowners and agents: "The attention of the Board of Trade has frequently been called to cases in which British vessels have been endangered or wrecked through the masters' attempting to navigate them by means of antiquated or otherwise defective charts. The Board of Trade desires, therefore, to direct the especial attention of shipowners and their agents to the necessity of seeing that the charts taken or sent on board their ships are corrected to the time of sailing. Neglect to supply a ship with proper charts will be brought prominently before the Court of Inquiry in the event of a wreck occurring from that cause."

The following is a translation of a notice in the preface to the catalogue of charts published by the German government: "Owners and masters of vessels are apprised that cases of marine accidents in which the casualty was due to antiquated or erroneous charts, have frequently been before the admiralty courts. In consequence of this, the 'Instructions for the prevention of accidents to steamers and sailing vessels,' issued by the Seeberufsgenossenschaft have been amended by the following additional paragraph: 'It is obligatory upon every master, except when engaged in local coastwise navigation, to keep the Notices to Mariners regularly, and with the aid of them to carefully keep his charts up to date.'"

The British shipping laws provide that a ship may not be sent to sea in such an unseaworthy state that the life of any person is thereby endangered, and the House of Lords has defined the term "seaworthy" to mean "in a fit state as to repairs, equipment, and crew, and in all other respects, to encounter the ordinary perils of the voyage." Proper charts and sailing directions are a necessary part of the equipment of a vessel, and the courts have frequently inquired into this.

The records of the British courts, however, show that even in recent years many ships have been damaged or lost owing directly or indirectly to failure to have the latest information on board. The following are instances from these records.

In 1890 the steamer _Dunluce_ was lost owing to the use of an old edition of the Admiralty chart which showed a depth of 4-1/2 fathoms on the Wikesgrund, whereas the later chart showed much less water. In this case the master had requested his ship chandler to send him the latest chart.

In 1891 the steamer _St. Donats_ got ashore on a patch which was not shown on the chart in use, which was privately published in 1881; the danger was, however, shown on the Admiralty chart corrected to 1889.

Also in 1891 the steamer _Trent_ was lost on the Missipezza Rock in the Adriatic. The ship was navigated by a private chart published in 1890 which did not show this rock, and by sailing directions published in 1866.

The steamer _Aboraca_, stranded in the Gulf of Bothnia in 1894, was being navigated by a chart corrected to 1881 which did not show that the Storkallagrund light-vessel had been moved eight miles.

The steamer _Ravenspur_ was lost on Bilbao Breakwater owing to the use of a chart not up to date which did not show the breakwater. In 1898 the steamer _Cromarty_ was lost in attempting to enter Ponta Delgada harbor, and in 1901 the steamer "Dinnington" was lost by steaming on to the new breakwater in Portland harbor; both of these disasters were likewise due to the use of old charts which did not show the breakwaters. In these three cases the masters of the vessels had authority to obtain the necessary charts at the owners' expense.

Not so, however, in the following case from the finding of a British marine court in 1877: "The primary cause of the ship's getting on shore was due to the master's being guided in his navigation by an obsolete Admiralty chart dated September 1, 1852, and corrected to April, 1862, and on which no lights are shown to exist either in ... or ... and to his not being supplied with the latest sailing directions. The Court, considering that the master was obliged to furnish himself with chronometer, barometer, sextant, charts, sailing directions, and everything necessary for the navigation of his vessel out of his private resources, which, under very favorable circumstances, might perhaps reach £150 a year, find themselves unable in this instance to pass a heavier censure upon him than that he be severely reprimanded."

The loss of the German steamer _Baker_ on the coast of Cuba on January 31, 1908, was declared by the marine court at Hamburg to be due in part to the use of an unofficial chart which did not show the latest surveys on that coast.

#Use the largest scale charts.# The largest scale chart available should be employed when entering channels, bays, or harbors, as it gives information with more clearness and detail, positions may be more accurately plotted, and sometimes it is the first corrected for new information.

The records of the courts of inquiry also show cases where vessels have been wrecked owing to the use of charts of too small scale.

In 1890 the steamer _Lady Ailsa_ was lost on the Plateau du Four. The only chart on board for this locality was a general chart of the Bay of Biscay, and the stranding was due to the master's mistaking one buoy for another. The court found that the chart, although a proper one for general use, was not sufficient for the navigation of a vessel in such narrow waters and on such a dangerous coast.

The _Zenobia_ was stranded on the San Thomé Bank in 1891. On this vessel the owners were to furnish the chronometers and the master the charts and sailing directions. The master was, however, apparently satisfied with only a general chart of the South Atlantic for navigation on the coast of Brazil, and had no sailing directions at all.

#The depth curves# on charts furnish a valuable guide, and if the curves are lacking or broken in some parts it is usually a sign that the information is incomplete. The 100-fathom curve is a general warning of approach to the coast. The 10-fathom curve on rocky coasts should be considered as a danger curve, and caution used after crossing it. The 5-fathom curve is the most important for modern vessels of medium draft, as it indicates for them the practical limit of navigation. The 3, 2, and 1-fathom curves are a guide to smaller vessels, but have less significance than formerly because of the increase of draft of vessels.

#The shrinkage of paper#, especially in plate printing, has been referred to. This introduces two possible sources of error: first, the shrinkage being different in the two directions, any scale printed on the chart will be accurate only when used in a direction parallel to itself; second, for the same reason, angles and directions will be somewhat distorted. Fortunately these errors are not serious in the ordinary navigational use of a chart, but they should not be overlooked when accurate plotting or measuring of distances is attempted on a plate-printed chart.

The actual shrinkage measured on charts printed from plates varies from 1/3 inch to 1 inch in a length of chart of 36 inches. On British and American plate printed charts the shrinkage is usually from two to nearly three times as much in one direction as it is in the other.

#Care of charts.# In order that they may be properly used charts should be filed flat and not rolled. They should be systematically arranged so that the desired chart can be instantly found. They should be cared for and when in bad condition replaced by new copies. They can be most conveniently filed in shallow drawers, thus avoiding the placing of many charts in a single drawer. The latter is a common fault; it not only increases the labor of handling the charts but adds to the liability of their injury.

PUBLICATIONS SUPPLEMENTING NAUTICAL CHARTS.

There are several publications in book and in chart form which are either necessary or convenient for use in connection with nautical charts. These comprise the coast pilots, notices to mariners, tide tables, light and buoy lists, and various special charts.

#Coast pilots#, or sailing directions, are books giving descriptions of the main features, as far as of interest to seamen, of the coast and adjacent waters, with directions for navigation. They contain much miscellaneous information of value to the mariner, especially the stranger. Although they contain additional facts which cannot be shown on the charts, they are not at all intended to supersede the latter; the mariner should in general rely on the charts. The sailing directions can be less readily corrected than the charts, and in all cases where they differ the charts are to be taken as the guide.

The most extensive series of sailing directions is that published by the British Admiralty, comprising fifty-six volumes and including all the navigable regions of the world. In the United States the Coast and Geodetic Survey publishes ten volumes of coast pilots for the Atlantic, Gulf, and Pacific coasts, Porto Rico, and southeastern Alaska, and eight volumes of sailing directions for Alaska and the Philippine Islands. The United States Hydrographic Office publishes sixteen volumes of sailing directions for various parts of the world.

#Notices to Mariners# are published at frequent intervals, giving all important corrections, which should be at once applied by hand to the charts, such as rocks or shoals discovered and lights and buoys established or moved. New charts, new editions, and canceled charts are also announced.

These notices should be carefully examined and the necessary corrections made on all charts of the sets in use on the vessel. A chart should be considered as a growing rather than a finished instrument, and constant watchfulness is required to see that it is kept up to date. Neglect of this may cause shipwreck, as the following instance shows. Report came to Manila in 1904 that there was a low sand islet lying off the very poorly charted northeast coast of Samar; this information was promptly published in the local Notice to Mariners. About a month later a small steamer was sent to land some native constabulary on that coast. The captain failed to obtain or observe this notice, and approached the coast before daylight on a course which led directly across the sand islet. The vessel was driven far up on the sand, where it still lies.

In the United States, weekly Notices to Mariners are published by the Department of Commerce and Labor for the coasts under the jurisdiction of the United States, and by the Navy Department for all regions. These notices are distributed free and can be obtained from chart agents and consular officers. In Great Britain the notices are published at frequent intervals by the Hydrographic Office, and practically all countries issuing charts also issue such notices. Information as to important changes in lights and other announcements of navigational interest are also sometimes printed in the marine columns of newspapers and in nautical periodicals.

#Tide Tables.# Brief information as to the time and height of the tide is usually for convenience given on the face of the chart. More complete information is published in the Tide Tables, with which every navigator should be provided. "The Tide Tables for United States and foreign ports," published annually in advance by the United States Coast and Geodetic Survey, give complete predictions of the time and height of high and low water for each day of the year for 70 of the principal ports of the world, and the tidal differences from some principal port for 3000 subordinate ports. The other leading nations also publish annual tide tables; those of the British government are entitled "Tide Tables for British and Irish ports, and also the times of high water for the principal places on the globe."

#Light and buoy lists.# Brief information as to all artificial aids to navigation is shown on the charts. Every vessel should also have on board the latest official light and buoy lists, which give a more detailed description than can be placed on the charts.

Light and buoy lists for the coasts of the United States are published annually by the Light-House Board. The United States Hydrographic Office publishes a "List of Lights of the World" (excepting the United States), in three volumes.

The British Hydrographic Office publishes eight volumes of Lists of Lights, and these are corrected annually.

#Chart catalogues# are published in connection with all series of charts. They give the particulars and price of each chart published, and are usually arranged in geographical order, with both alphabetical and numerical indexes, for convenience in finding charts either by position, name, or number.

#Charts for special purposes.# There are various special charts published for the benefit of mariners, although not intended for direct use in plotting the course of a vessel or in locating its position. Some of the more important of these are mentioned below.

#Gnomonic charts# are intended solely for laying down the great circle or shortest practicable courses between points, for which purpose they are very convenient. Their use has already been described. The United States Hydrographic Office publishes six such charts, for the North Atlantic, South Atlantic, Pacific, North Pacific, South Pacific, and Indian Oceans.

#Current charts# are published by the British Hydrographic Office for the various oceans; these usually show the average ocean currents, but for the Atlantic there are monthly and for the Pacific quarterly current charts.

#Magnetic variation charts# are published by both the United States and British governments. They show on a mercator chart of the world the isogonic lines, or lines along which the variation of the needle from true north is the same. The lines are drawn for each degree of variation. The annual change in the variation is also indicated.

Other magnetic charts are published showing the lines of equal magnetic dip, horizontal magnetic force, and vertical magnetic force.

#Meteorological ocean charts# are published by several governments, including the United States, Great Britain, and Germany, and give the average weather conditions, winds, fogs, currents, ice, tracks of storms, and other information. "Pilot charts" of the North Atlantic and North Pacific Oceans are issued by the United States Hydrographic Office about the first of each month, and give "a forecast of the weather for the ensuing and a review of that for the preceding month, together with all obtainable information as to the most available sailing and steam routes, dangers to navigation, ice, fog, derelicts, etc., and any additional information that may be received of value to navigation." Mariners in all parts of the world have joined in contributing the information which has been used in compiling these pilot charts.

#Track charts# are published by the British and United States governments. That of the latter is entitled "Track and distance chart of the world, showing the routes traversed by full-powered steamers between the principal ports of the world, and the corresponding distances."

#Telegraph charts# are published showing the "telegraphic connections afforded by the submarine cables and the principal overland telegraph lines."

#Index charts# are outline plans showing the area covered by each chart of a series, and furnish a convenient means of finding a chart of any desired region or of selecting the most suitable chart for any purpose. These index charts are published either in sets, showing all the charts of a series, or are bound into the chart catalogues.

#Star charts# are included in navigational series, and are conveniently arranged for use on shipboard in identifying the brighter stars. The United States Hydrographic Office publishes two, constellations of the northern and of the southern hemispheres.

#Explanatory sheets# are published in connection with various series of charts, giving explanations of the symbols and abbreviations used and of other important features. In the United States the Coast and Geodetic Survey has issued a small pamphlet, "Notes on the use of charts," which contains explanations of its chart symbols, and the Hydrographic Office has published "A manual of conventional symbols and abbreviations in use on the official charts of the principal maritime nations."

INDEX

PAGE

Aids to navigation, 118

Arbitrary projection, 79

Astronomical observations, 32

Astronomical positions, 126

Bearings, position by, 130

Board of Trade notice, 148

Care of charts, 153

Catalogues of charts, 157

Changes in the coast, 98

Chart making, development of, 6

Chart publications of various nations, 18

Charts, earliest nautical, 6

Charts, loxodromic, 7

Charts, plain, 8

Chart schemes, 67

Chart working, 124

Coast and Geodetic Survey, United States, 13

Coast pilots, 154

Compass bearings, 130

Compass, nautical use of, 6

Compass, variation of, 7

Compilation of information, 67

Correction of charts, method of, 110

Cosa, Juan de la, 8

Current charts, 157

Currents, 50, 121

Danger angle, horizontal, 136

Danger bearing, 131

Danger range, 132

Dangers, reports of, 56

Dates on charts, 123

Dead reckoning, 129

Depth curves, 116, 152

Depths, unit for, 19, 116

Depth units, relation of, 118

Directions on charts, 115

Distances, measured on chart, 125

Distribution of charts, 96

Doubling angle on bow, 131

Draft of vessels, 97

Dragging for dangers, 55

Earthquakes, 109

Electrotyping plates, 89

Elevations, 122

Engraving machines, 89

Engraving on copper, 84

Engraving on stone, 93

Eskimo map, 1

Etching on copper, 95

Explanatory sheets, 159

Flattening of the earth, 3

France, establishment of chart office, 10

Geographic position on charts, 115

Geography, early, 2

Germany, contributions to hydrography, 14

Gnomonic charts, 79, 157

Gnomonic projection, 74

Great Britain, contributions to geography, 14

Holland, development of chart making, 10

Hydrographic Office, British, 13

Hydrographic Office, United States, 13

Hydrography, 40

Index charts, 158

Information on charts, 23

Instruments used on charts, 141

Lake Survey, United States, 13

Largest scale chart, 151

Latest editions of charts, 148

Light and buoy lists, 156

Lithographic printing, 94

Locating a vessel, 126

Longitude, initial, 19

Longitude, uncertainties in, 10

Magnetic charts, 157

Magnetic variation, 56

Map, earliest, 2

Map making, development of, 2

Maps, need of, 1

Maritime surveys, extension of, 17

Mercator chart, history, 8

Mercator projection, 68

Meteorological charts (pilot charts), 158

Navigation, use of charts in, 124

Notices to mariners, 111, 155

Paper, shrinkage of, 152

Parallel rulers, Field's, 141

Photolithography, 93

Plane of reference, 20, 119

Plotting positions, 124

Polyconic projection, 73

Printing, plate, 84, 90

Privately published charts, 21

Progress of hydrographic surveys, 17

Projection, explanation of, 114

Projections, 68, 114

Protractor, three-arm, 144

Ptolemy, 3

Publication of charts, methods, 84

Purpose of charts, 22

Ranges, 132

Reading charts, 112

Reliance on charts, 144

Reports of dangers, erroneous, 57

Requirements for charts, 23

Revision of charts, need of, 97

Rock, Brooklyn, 50

Sailing directions, early, 4

Sailing directions, 154

Scale equivalents, 113

Scales of charts, 79, 112

Set, graphical allowance for, 125

Sextant angles, 132

Sheets for surveys, 39

Shrinkage of paper, 152

Sound, position by, 140

Sounding machines, 49

Soundings, position by, 136

Star charts, 159

Station pointer, 144

Steamer for surveying, 49

Sumner's method, 126

Supplementary publications, 154

Surveys on foreign coasts, 14

Surveys, need of thorough, 31

Symbols on charts, 20

Telegraph charts, 158

Three-point problem, 132, 135

Tides, 50, 120

Tide tables, 156

Topography, 39

Topography on charts, 123

Track charts, 158

Triangulation, 32

Uniformity in charts, 21

Use of charts in navigation, 124

Vertical angles, 139

Vigias, removal of, 62

Vigilance, need of, 140

Volcanic action, 109

Wrecks due to deficient charts, 149

SHORT-TITLE CATALOGUE
OF THE
PUBLICATIONS
OF
JOHN WILEY & SONS,
NEW YORK.
LONDON: CHAPMAN & HALL, LIMITED.

ARRANGED UNDER SUBJECTS.

Descriptive circulars sent on application. Books marked with an asterisk (*) are sold at _net_ prices only. All books are bound in cloth unless otherwise stated.

AGRICULTURE.

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