The lead, as you know, is used to ascertain the depth of the water and, when necessary, the character of the bottom. There are two kinds of leads: the hand lead and deep-sea lead. The first weighs from 7 to 14 pounds and has markings to 25 fathoms. The second weighs from 30 to 100 pounds and is used in depths up to and over 100 fathoms. Put in your Note-Book:
Fathoms which correspond with the depths marked are called marks. All other depths are called deeps. The hand lead is marked as follows:
2 fathoms - 2 strips of leather.
3 fathoms - 3 strips of leather or blue rag.
5 fathoms - A white rag.
7 fathoms - A red rag.
10 fathoms - A piece of leather with one hole in it.
13 fathoms - Same as at 3.
15 fathoms - Same as at 5.
17 fathoms - Same as at 7.
20 fathoms - 2 knots or piece of leather with 2 holes.
25 fathoms - 1 knot.
30 fathoms - 3 knots.
35 fathoms - 1 knot.
40 fathoms - 4 knots.
And so on up to 100 fathoms.
The large hand leads are hollowed out on the lower end so that an "arming" of tallow can be put in. This will bring up a specimen of the bottom, which should be compared with the description found on the chart.
All up-to-date sea-going ships should be fitted with Sir William Thompson's Sounding Machine (see picture in B. J. Manual). This machine consists of a cylinder around which are wound about 300 fathoms of piano wire. To the end of this is attached a heavy lead. An index on the side of the instrument records the number of fathoms of wire paid out. Above the lead is a copper cylindrical case in which is placed a glass tube open only at the bottom and chemically colored inside. The pressure of the sea forces water up into this tube, as it goes down, a distance proportionate to the depth, and the color is removed. When hoisted, the tube is laid upon a prepared scale, and the height to which the water has been forced inside shows the depth in fathoms on the scale.
DIVIDERS
The dividers are nothing but an instrument for measuring distances, etc., on the chart.
THE LOG
There are two kinds of logs - the chip log, used for measuring the speed of the ship, and the patent log, used for measuring distance run.
The chip log consists of a reel, line, toggle and chip. Usually a second glass is used for measuring time. The chip is the triangular piece of wood ballasted with lead to ride point up. The toggle is a little wooden case into which a peg, joining the ends of the two lower lines of the bridle, is set in such a way that a jerk on the line will free it, causing the log to lie flat so that it can be hauled in. The first 10 or 15 fathoms of line from the log-chip are called "stray line," and the end of this is distinguished by a mark of red bunting. Its purpose is to let the chip get clear of the vessel's wake. The marks on the line (called knots) are pieces of fish line running through the strands of the reel line to the number of two, three, four, etc. A piece of white bunting marks every two-tenths of a knot. This is because the run of the ship is recorded in knots and tenths. The knots of fish line are 47 feet 4 inches from each other.