SOUNDING, the operation of trying the depth of the sea and the nature of the bottom, by means of a plummet sunk from a ship to the bottom. There are two plummets used for this purpose; one of which is called the hand·lead, weighing about eight or nine pounds; and the other the deep-sea lead, which weighs from twenty-five to thirty pounds; and both are shaped like the frustum of a cone or pyramid. The former is used in shallow waters, and the latter at a great distance from the shore, particularly on approaching the land after a seavoyage. Accordingly the lines employed for this purpose are called the deep-sea lead line, and the handlead line. The handlead line, which is usually twenty fathoms in length, is marked at every two or three fathoms; so that the depth of the water may be ascertained either in the day or night. At the depth of two or three fathoms there are marks of black leather; at five fathoms, there is a white rag; at seven, a red rag; at ten, black leather; at thirteen, black leather; at fifteen, a white rag; and at seventeen, a red rag.

Sounding with the handlead, which by seamen is called heaving the lead, is generally performed by a man who stands in the main chains to windward. Having the line quite ready to run out without interruption, he holds it nearly at the distance of a fathom from the plummet; and having swung the latter backwards and forwards three or four times, in order to acquire the greater velocity, he swings it round his head, and thence as far forward as is necessary; so that by the lead’s sinking while the ship ad vances, the line may be almost perpendicular when it reaches the bottom. The person sounding then proclaims the depth of the water, in a kind of song resembling the cries of hawkers in a city. Thus, if the mark of five fa thoms is close to the surface of the water, he calls, “By the mark five ;” and as there is no mark at four, six, eight, &c< he estimates those numbers, and calls, “By the dip four,” &c. If he judges it to be a quarter or an half more than any particular number, he calls, “And a quarter five, and a half four,” &c. If he conceives the depth to be three more than a particular number, he calls it a quar ter less than the next: thus, at four fathoms and three fourths he calls, “A quarter less five.”

The deep-sea lead is marked with two knots at twenty fathoms, three at thirty, and four at forty, and so on to the end. It is also marked with a single knot in the mid[7:20:487] cle of each interval, as at twenty-five, thirty-five, forty-five fathoms, &c. To use this lead more effectually at sea, or in deep water on the seacoast, it is usual previously to bring to the ship, in order to retard her course: the lead is then thrown as far as possible from the ship on the line of her drift, so that, as it sinks, the ship drives more perpendicularly over it. The pilot, feeling the lead strike the bottom, readily discovers the depth of the water by the mark on the line nearest its surface. The bottom of the lead being also well rubbed over with tallow, retains the distinguishing marks of the bottom, as shells, ooze, gravel, &c. which naturally adhere to it. The depth of the water, and the nature of the ground, which is called the soundings, are carefully marked in the logbook, as well to determine the distance of the place from the shore, as to correct the observations of former pilots.