The steel schooner Thomas W. Lawson, the largest American sailing vessel. Launched

by the Fore River Ship and Engine Company, July 10, 1902.

A change

ters which may or may not have changed their rate. in rate of the chronometer or other errors, which will affect the ship's position materially, may thus be ascertained, and should thick weather come on later, the navigator would be in a better position to take the ship safely to her port or destination. Again, should there be any doubt as to longitude, and it was found impracticable to make any point of land, it may be best to make the latitude of the place required and then if possible run on a parallel. The safe way is to locate the ship on a Sumner's line and know to a certainty the relative bearing of the land, which will determine the course; should thick weather be immediately threatening and close in, the navigator would at least know where he is and whether or not danger was near. Of course due regard should always be given to soundings, and even in working your way into an unknown harbor in clear weather, soundings are of infinite value to the navigator. Sumner lines, chronometers, etc., will be taken up shortly and fully explained; also the currents, the time of tide, as well as other facts laid down in the sailing directions, must be considered.

The Method of Sounding. Sounding is the operation of finding the depth of water and the nature of the bottom by means of a lead weight. Two leads are used for sounding,- a hand lead weighing from 7 to 14 pounds, with a line marked to 20 fathoms, and a deep sea lead weighing from 40 to 100 pounds, with a lead line about 100 fathoms in length. A hand lead weighing about 10 pounds is about all one man can easily handle, and is of use only in shallow water; as, for instance, in making a harbor. If the ship is making 7 knots or more, it takes a good leadsman to get bottom with a hand lead in 10 fathoms.

Deep sea leads, as the name implies, are for getting soundings in deep water. It is necessary when using an ordinary deep sea lead of about 40 pounds to heave the ship to; previous to heaving to, the line is reeled off until there is sufficient amount of loose line to reach bottom, and the lead carried forward. The cavity in the bottom of the lead is filled with grease or soap, which catches and retains a sample of the bottom.

Deep sea sounding in this manner is a clumsy operation, and at present is but seldom used. An improved method is the use of

Lord Kelvin's Patent Sounding Machine, shown in Fig. 9. Piano wire wound on a drum is used for the lead line; this makes it possible for the lead to descend much quicker. With this machine it is claimed that bottom can be reached at 100 fathoms, with the ship making 14 knots or more. A glass tube descends with the lead; this tube is hermetically sealed at the top end and open at the botThe interior of the tube is covered with a chemical prepara

tom.

Fig. 9.

tion, which changes color when salt water touches it. As the lead sinks deeper and deeper, the pressure becomes greater and greater, and the air in the tube is compressed as the salt water is forced in. The discoloration of the chemical shows exactly how high the water rose in the tube, and the depth found by means of the scale (graduated to fathoms) attached to the side of the tube. In addition there is a small hand moving over a dial, which also indicates the amount of wire unwound.

For purposes of navigation no importance can be placed upon a single cast of the lead; the proper method to follow in sounding is as follows: Take soundings at regular intervals, say every 4 or 5 miles; mark a strip of paper so that the distance between the marks is 4 or 5 miles, as the case may be, using of course the chart best suited for the purpose, from which the 4 or 5 mile inter

EDGE OF PAPER

28 16 30 32 45 47 44 30 24

FINE GRAY
SAND

Fig. 10.

vals may be taken. Now as each successive cast is made, the depth and nature of the bottom should be marked on the strip of paper, thus obtaining a series of soundings. The bit of paper will resemble Fig. 10. Now with this strip of paper move about the chart in the locality where the vessel is thought to be, and have the edge of the paper run or point in the same direction as

the ship is steering true. The soundings on the paper will be found to approximate those on the chart, some places much more closely than others. It requires experience and practice to decide just where the ship is, particularly if it has been running on dead reckoning for several days. Of course in continued thick weather it is more difficult to be absolutely sure of your position by soundings, but nevertheless they are valuable, and may prove that you are not where you think you are.