There is a hollow at the heel of a lead which can be filled—armed as it is termed—with tallow; a specimen of the bottom—mud, sand, or shingle—is brought up with the lead, and this, by reference to the chart, which generally marks the nature of the bottom, may enable us to find our position.
CHAPTER XIII.
HOW TO FIND ONE’S WAY AT SEA.
Cross bearings—Tacking across the sea—Leeway—How to allow for a current—To find the hour of high water.
Having in the last chapter described the various instruments which enable a mariner to direct his course, we will now give some further explanations of the method of employing the chart and compass.
Cross Bearings.—When a vessel is in sight of land, her position can be calculated with exactness by several methods.
First. By cross bearings of two known objects. If two well-known landmarks are visible on shore, we observe how each of them bears by our compass. We then refer to the chart, lay down these bearings with the parallel rule, and the point where the lines cut will represent the vessel’s position.
Fig. 47.
For instance (see ([Fig. 47]), the beacon A is found to be N.W. of us, the beacon B N.E. of us. We lay our parallel rule on the magnetic compass design on the chart so that its edge passes through N.W. and also through the centre of the compass. We then slide the rule to the beacon A on the chart—preserving the direction—and draw with a pencil the line from A indicated by the edge of the rule.