Sailing in my yacht, I saw a lighthouse bearing E. by N., and, after sailing 14 miles N. by W., it bore S. E. Required the distance of the yacht from the lighthouse at both stations.
Solution.—Describe the compass E. S. W., and let its centre X represent the place of the yacht at the first station; draw the N. by W. line, X Y, equal to 14 miles, and Y will represent the second station.
Draw the line E. by N., X Z, of an indefinite length, and the line Y Z parallel to the S. E. and N. W. line of the compass: the point of intersection Z will represent the place of the lighthouse, and the distance Y Z, being measured by the same scale of equal parts with which the 14 miles of course is laid off, will be found to be 16-3/4 miles, and X Z 9-1/4 miles.
USE OF THE CHARTS.
Charts can be purchased, at a very reasonable rate, of all the important harbors and the whole coast-line of the United States. They come nicely backed with cloth, so as to stand considerable hard sea-usage. They should be kept, when not in use, rolled up in a large tin box made for the purpose, or a long, narrow wooden trunk, called a chart-box.
In using charts, great care should be taken to see whether or not the courses laid down to be sailed are magnetic ones; that is, with the variation of the compass allowed. Such is usually the case; but there are charts made where the variation of the compass must be allowed to make the courses true.
Always carefully read all the notes upon the margins of a chart: one will often run across an item of the greatest interest or importance. Nearly all charts of harbors and the coast-line will be found with two scales of miles upon them; one being marked statute miles, and the other nautical miles.
Now, the difference is this, the scale that is marked statute miles means a mile of 320 rods of 16-1/2 feet each, or 1,760 yards of 3 feet each, or 5,280 feet; whilst a nautical mile means the sixtieth part of a degree of the earth's surface measured at the equator, which is about 6,086.4 feet in length.