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as it is frequently termed. The Dead Reckoning is an account of the ship's circumstances from the noon of one day to the noon of the next, which account is hourly kept on what is called the log-board, the contents of which are termed the log,—the working it off, the day's work.

When we read from the log that the ship at noon was close in at the Lizard Point, and that until 3 P.M. she sailed W. at 6 knots or miles an hour, it is a very simple operation to discover that she may be 18 miles W. of the Lizard. But when we have to take into the account the variation of the compass, the force and direction of the tide, and the quantity of leeway, the investigation becomes more complex. What is required to be accurately learnt is, the true rate at which the ship changes her place, and the real direction or course she takes.

Supposing the Patent, or other log, to denote a speed of 7 knots an hour, it by no means follows that the ship is making good that rate; for should she be going against a tide flowing 3 knots an hour, the vessel has changed her place by only 4 knots; and conversely, should she have had a similar tide in her favour, she has accomplished a distance of 10 miles; this deduction or addition of the rate of tide must be alone guided by experience, the force of the stream varying at every hour of the tide. When the ship is well out at sea, she is not affected by the tide, as it creates no stream; in the open ocean the tidal wave sweeping along, but causing no more current than an ordinary billow. But, on the other hand, ocean currents exist independently of all tide, and are sometimes constant, sometimes variable, both in strength and direction. These probably have been as disastrous to shipping as they are practically imperceptible, and to be detected

only by the ship's place found by Observation being widely different from that by Account. Should you be becalmed, a boat may be put out, from which is lowered to a great depth some heavy weight; when, the boat remaining as still as though it was anchored, by observing the course and drifting of the ship from the boat, an estimate may be formed of the direction and velocity of the current.

The estimated current should be carefully noted in the log; also the quantity of leeway, as a quarter, half, or whole point of the compass, attached to the course on which it is made; the direction of the wind and hourly rate of sailing; not forgetting the variation for the locality you are navigating; and the deviation of the compass if the ship is of iron, or composite.

A DAY'S WORK.

The reader is now assumed to have a clear understanding of the preparatory work of Navigation, and I shall proceed to the day's work.

There are two kinds of days—the astronomical or seaman's day, and the civil or landsman's day. The latter commences at midnight, and terminates at the following midnight, being divided by noon, the time before noon being noted as A.m. (ante-meridiem), the latter division being noted as P.m. (post-meridiem).

With the astronomical day it is always P.m.; for, instead of from midnight, it commences at noon, and continues until the succeeding noon. Thus, what a landsman or civil time would indicate by June 21st, 3 hours A.m., i.e. 3 hours after midnight, the sailor or the Nautical Almanac would express as June 20, 15 hours; but this latter expression will not come into use until we are required to find our longitude by chronometer, as explained farther on.

In keeping the log, the day, as already observed, commences at noon, and terminates on the following noon. The hours are placed in succession, but instead of carrying them on to 24, they recommence after 12, in accordance with tho arrangement of time-pieces. The first figure put down on the log-board is 1, meaning one o'clock. Whatever then is written down to that figure indicates what has occurred from tho previous hour up to that hour: thus, the first line of the following table indicates that from noon to one o'clock the

H. K. F. Courses. Winds. Leeway. Remarks.

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H. K. F. denote the columns appropriated to the hours, knots, and furlongs made good during these hours.

ship has sailed 4 knots (or miles) and 2 furlongs (mile); the course was West by compass, the leeway amounted to one point and a quarter of the compass, which must be allowed from the S.S.W. wind which was blowing. Again, the last line of the table indicates that from 8 till 9 o'clock the ship sailed 5 knots and 6 furlongs, steering by the compass a S.W. b W. course, with one and a half points of the compass to be allowed for leeway from the wind. And similarly for

other hours through the 24.

This to the learner may at first appear to be somewhat puzzling, but it will soon cease to be so, if taken in its proper time.

Ex. Supposing a ship has sailed true S.W. 80 miles from the Land's End, we thus set about to find her place on the chart.

1. By Inspection.-Enter Trav. Tab. 4, with course, 4 points (S.W.) and 80 miles of dist.; we get diff. lat. 56.6' S. and dep. 56.6′ W.

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Entering Tab. 5 with mid. lat. 49° as a course and dep. in lat. column we get 87' as diff. long. in dist. column.

Or, in Tab. 4, entering with course 4 points (S.W.) and merid. diff. lat. 88 in lat. column, we get 88 as diff. long. in dep. column.

Then, (Land's End) long. left 5° 43′ W.
Diff. long. 87' W.=1 27 W.

By Mid. lat.; Long. in 7 10 W.

Hence a true S.W. course and run of 80 miles from the Land's End brings us into Lat. 49° 7' N., Long. 7° 10' or 7° 11′ W., according to whether we take Middle Latitude or Mercator Sailing; and this position you can prick on the chart.

We shall now proceed to show the method by Construction. With the pencil-compass we form any conveniently sized circle; then, drawing two diameters cutting each other at right angles, the four extremities now represent the cardinal points of the compass (see fig. 3).

Each quarter of the mariner's compass is divided into 8 points, and we now set the pointed compasses so that the space between their points shall equal an eighth of a quarter of this compass; in other words, one point being on s, the portion of the circle between S and contains just eight of the spaces between the

points of the steel drawing compass. Now S.W. (the ship's true course) is south, 4 points towards the west. Place the compasses then on S, and count off 4 points in the direction of to a; b will represent the point sailed from, or the Land's End,—b a, the true course steered. From b through a draw a line of any convenient length, and from the scale on the protractor take with the compasses a space equal to 80 miles, which prick off from b on the line b a. We will suppose c to be the

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point to which the compasses reach, and which will now represent the ship's place. From this point draw cd at right angles to b 8 produced any length to meet it; or, which is the same thing, parallel to the line W E; to do which, place the parallel ruler along W E, and work it to c, and draw from c the line e d. This triangle will now exhibit the following: the angle cbs formed by the lines bc, bd, will be the course made good; bc, the distance made good; bd, the difference of latitude; and dc, the departure, which

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