By following the above simple directions intelligent seamen have frequently been able to make valuable additions to existing charts, and rough work of this description is always most acceptable to the Hydrographic Office of the Admiralty, and infinitely more valuable than finished drawings, that may, or may not, be founded on facts.

SOUNDING.

A VESSEL may, at times, be anchored in a bay or off a coast of which no chart exists; in this case it may be considered necessary, not only to sound round the ship, but to be able to make some report upon the anchorage. If, therefore, time, opportunity, or inability, does not admit of making a survey of a harbour, an idea of its form, extent, and depth of water, may be arrived at by simply running lines of soundings from the ship, anchored near the centre, to the prominent points, noting at these points the masthead angle, taken both on and off the arc, and the compass bearing of the ship.

*

In such a case a flag or black ball should be hoisted close up to the ship's main truck, to facilitate the taking of the masthead angle, and the following practical hints on sounding may be found useful.

Sounding is especially work for a sailor, requiring all the ready wit and tact of his profession. In sounding, the sailor has to manage air and water, the rise and fall of the tides, the velocity of currents, and to fit in his work to suit wind and weather; these forces becoming firm allies to the man who studies them, and foes only to him who knows not how to use them.

The instruments, by the help of which the important operation of sounding is carried on, are the sextant and lead line.

*If shoals are discovered in harbours or roadsteads, or upon coasts where the chart furnishes the sailor with reliable points upon the shore, the soundings should, in such cases, be fixed by sextant angles taken to such points. Sounding by masthead angle should only be used if no reliable positions can be found, or if time does not permit of making a rough triangulation of the place. The necessary geometry for determining positions by sextant angles will be found at page 178. Sailors who may wish to gain a further insight into Practical Nautical Surveying, are referred to a small work on that important subject, by Staff-Commander Thomas A. Hull, R. N., Superintendent of Admiralty Charts; published at 28., by J. D. Potter, Poultry, E.C.

The Sextant, a now common but no less invaluable instrument, the inventor of which may be looked upon as one of the greatest benefactors to mankind, might be considered by the sailor as the tongue of his profession, without which he would be, to a certain extent, dumb, and able only indistinctly to give utterance to his discoveries. The sailor should therefore lose no opportunity of making himself thoroughly conversant with this useful instrument, understanding all its adjustments, peculiarities, causes of error, the size of angles to be safely measured with it, and the means of re-quicksilvering its reflectors. With the assistance of the sextant, Captain Moriarty found the lost end of the Atlantic cable, and without it no ocean can be properly sounded or telegraph cable fairly laid.

When in port, lying at anchor, a simple exercise in using the sextant is to take a round of angles, consisting of six or more, between distinctly seen objects lying nearly in the same horizontal plane, and see how near in addition they may be brought to 360°. Handle the sextant both ways, inverted as well as direct; many objects from being indistinct cannot be reflected from right to left, and the left hand object that can be reflected, must in such case be used.

Every opportunity should be taken of fixing the ship on the chart by bearing and angle. Taking it for granted that the harbour in which the vessel is anchored is well surveyed, it is good practice to take angles to the different points, peaks, and islets, and laying the same off from the ship's position, to see if they agree with those on the chart. True bearings of objects, both right and left of the sun, should be frequently observed, taking care that the angle measured between the sun and the object, is always double the altitude of the sun.

If angles are taken between two objects close to each other, care should be taken that they are on the same level, or that the angle measured is nearly horizontal; with large angles, it is of little consequence that the objects used are not on the same level, as the error caused by obliquity is in these cases small.

The Arc of Excess.-It is good practice to measure small angles off as well as on the arc; the arc of excess in most sextants is 5°. Observed masthead angles will generally be less than 5°, and

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angles of elevation taken to peaks on making the land will always be less than 5. Taking the angles off and on the arc, adding them together, and dividing by 2, gives an angle free of index error. sea, measuring the sun's semi-diameter, and comparing that obtained with that given in the Nautical Almanac, renders the observer dexterous in observing small angles with the sextant. If the object is clear and well defined, the inverting tube will be found of great assistance.

A man-of-war's man should lose no opportunity of volunteering to lay out targets in well-known harbours or roadsteads by the masthead angle, taking the angle both off and on the arc of the sextant, that being one of the methods used in nautical surveying for determining an approximate base. When the target is moored, if time permits, get a round of angles from it; these plotted on the plan of the harbour will afford an opportunity of testing the accuracy of the base obtained from the masthead angle, taking care to fix the ship's position for the way in which she may be swung, either on leaving or returning on board.

Admiral Sir E. Belcher gives the following detailed directions for re-silvering sextant glasses when injured by damp or wet :

"The requisites are clean tinfoil and mercury, a hares' foot is handy, lay the tinfoil, which should exceed the surface of the glass by a quarter of an inch on each side, on a smooth surface (the back of a book), rub it out smooth with the finger, add a bubble of mercury about the size of a small shot, which rub gently over the tinfoil until it spreads itself and shows a silvered surface, gently add sufficient mercury to cover the leaf, so that its surface is fluid. Prepare a slip of clean paper the size of the tinfoil. Take the glass in the left hand, previously well cleaned, and the paper in the right. Brush the surface of the mercury gently to free it from dross. Lay the paper on the mercury, and the glass on it. Pressing gently on the glass, withdraw the paper. Turn the glass on its face, and leave it on an inclined plane to allow the mercury to flow off, which is accelerated by laying a strip of tinfoil as a conductor to its lower edge. The edges may, after twelve hours' rest, be removed. In twenty-four give it a coat of varnish, made from spirits of wine and red sealing

wax."

The Lead line, by means of which the soundings are obtained, should be looked upon, and treated, as a valuable instrument, and therefore to be used for no other purpose but sounding, except in the absence of a chain for measuring a base line, or ascertaining the height of a cliff.

A good plan is to take for this purpose a ship's line that has been some little time in use, and is, therefore, well stretched, marking it when wet, to feet as far as 5 fathoms, on the same principle that the ordinary line is marked to fathoms, with two knots at 20 feet, and a bit of leather at 4 fathoms or 24 feet. The line should always be measured on the nails driven into the quarter-deck for that purpose, both when leaving and returning to the ship, taking care when measured that the line is always thoroughly wet. If obliged to use a new line, and shoal water is found in sounding out a bay or roadstead, the line should be re-measured in the boat, on the boathook, marked to feet, for that purpose. The line should always be

marked from the heel of the lead.

Men should be accustomed to heave the lead from the boats, and should be narrowly watched when first at work, in order to ensure their giving the correct soundings. The foremast awning stanchion, shipped, forms a good support for the leadsman's breast-rope. Some little practice and method is required on the part of the man heaving the lead from the boat, and also on the part of the officer, to determine, first when an "up and down" cast can be obtained without laying on the oars, and secondly, when it may be necessary to stop the boat altogether.

In the boat, as in the ship, the end of the lead line should always be secured before beginning to sound, and care should be taken that a "boat's lead" is taken from the ship for this work, with the necessary tallow for arming, as the nature of the bottom should always be noted, especially marking any changes that may occur, such changes often giving warning of neighbouring shoals.

Sounding in a tide-way it may be necessary to anchor the boat to obtain the masthead, or other angles, to fix the boat's position.

Noting. The soundings should be noted at equal intervals and distances. If a patent log cannot be obtained, this must be done

Under

by the judgment of the officer, by time or strokes of the oars. 5 fathoms the lead should be hove continously, and the boats position fixed by masthead angle of ship near the 3 and 5 fathom line at low water on approaching and leaving the land.

A space must be left underneath the figures of the soundings in the note book, in which they be reduced to low water by a table derived from observations made on the tides.-See page 167. The reduced soundings should be noted in red ink.

The time should be noted whenever soundings are taken, or at least every half-hour. In the absence of a watch the signal man on board the ship should be directed to hoist a numeral flag every hour, showing the number of the bells struck, keeping the same flying for five minutes, and hoisting the dinner pendant at noon. Attention in the notation of the time is not only a great assistance to the memory when plotting the soundings on a rough plan, but without it the reduction of the soundings to low water, cannot be honestly carried out.

The greatest care should be taken in entering the soundings, bearings, masthead angles, time, and other matters in the note book in such an intelligible manner, that another sailor could use them, so that in case of accidents, common to seamen, if the note book were saved, the work would not be lost. On return to the ship the work should be plotted as soon as possible, while the memory is green. Such precautions, adapted to the simple capacity of the industrious, enable the sailor to prove beyond a doubt the correctness of his work, and the existence of rocks, or errors in the chart, which his useful labours may have detected.

To ensure the lines sounded upon being straight lines, the ship should either be kept in transit with some object beyond her, or some well-marked object should be found on the shore in line or transit with the point or mark for which it is intended to steer, this second mark lying sufficiently far behind the point steered for to show any deviation from the straight line required. If pulling or sailing to seaward, the same should be looked for astern; such objects kept in transit must insure a straight line being followed; on nearing the shore a good look-out should be kept for a third object in the same