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We have refined here, which is not generally necessary: it would have been sufficient to have taken Mid. Lat. 50°.

And these results would be entered in the Log-Book in something like the following form, beneath the day's (24 hours) transactions :—

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Where there is no deviation of the compass, there is no absolute necessity, under ordinary circumstances, to correct the courses for variation, until you have arrived at a Diff. Lat. and Dep. from the courses corrected for leeway; it saves trouble and the result is equally accurate.

The following is the Day's Work just solved;-the courses are corrected for leeway, and with the distances, a Diff. Lat. and Dep. are found in the usual way; then this Diff. Lat. and 'Dep. give a Course and Dist. (1):-Now correct the course (just obtained) for Variation, once for all, and you get the True Course (2); -with the True Course and Dist., get the True Diff. Lat. and True Dep. (3); and the remainder of the solution is as before.

This method is inapplicable where the magnetic meridians are crowded together, so that the variation at the end of the day differs 3° or more from what it was at the commencement.

N.B.-The figures in this method (below) are as many as by the former one, but you remember we have not been at the trouble of correcting each course separately for variation.

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Mid. Lat. 50° and Dep. 91-2 (in Lat. col.) give in Trav. Tab. II. Dist. 142, which is

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DAY'S WORK No. 2.

Has leeway, deviation, and variation; and the solution is by correcting the courses, 1st, for leeway (if any); then for deviation; and lastly, for variation ;unless you correct by the error of the compass, that is, taking deviation and variation together as shown on p. 22-23.

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Diff. Lat. 86·5 S. and Dep. 17·1 W. in Trav. Tab. I. give Course made good S. by W., and Dist. 88 miles.

And our Log-Book form would be entered as follows:

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I have filled in a Lat. and Long. by observation to show that at the end of the next day (24 hours), when working up the reckoning, they will be taken as our departure Lat. and Long. Thus, suppose our Courses and Distances for the 24 hours gave us Diff. Lat. 72'-9 S., and Dep. 143'6 W.

Then, with these we get Course made good S. 63° W. and Dist. 161 miles also

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Mid Lat. 50° and Dep. 143'6 (in Lat. col.) give Diff. Long. 226, by searching Trav. Tab. first for 50° and then 51°, and taking the mean.

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A SHIP'S RECKONING.

A SHIP'S RECKONING is that account by which it can be known at any time where the ship is, and on what course or courses she must steer to gain her port. The basis of the reckoning is first kept on the Log-Board, and then transferred to the Log-Book.

The LOG-BOARD is a slate in a folding frame, on which is written at intervals during the day everything connected with the progress of the ship on her voyage, as well as any occurrences worthy of notice. The log-board is divided into seven columns as follows, under the headings of—

| H. | K. | F. | Courses.

Winds. | Leeway. | Remarks, Monday, April 10th. | The column on the left contains the 24 Hours from the noon of one day to the noon of the next, divided into two portions of 12 hours each.

In the second and third columns are the Knots and Fathoms (or Knots and

Tenths) the ship is found to run per hour, set against the hours when the log was hove. N.B.—The log is generally hove once in two hours, and the intervening rate inferred.

The fourth column contains the Courses the ship steers.

The fifth column gives the direction of the Winds.

The sixth column notes the Leeway, when any has been made.

The seventh column, for Remarks, gives ;—the kind of wind and weather-as moderate, fresh, gale, squally, strong gale, foggy, cloudy, &c.; the state of the sea as smooth, moderate, high, or heavy, &c.; the alteration of the sails-as tacked ship, squared the yards, &c.; the business doing aboard, as to the employment of the crew; when the ship was pumped, and the water in the well; the ships sighted or spoken; if in soundings, the depth of water and nature of the bottom, &c.; and what other remarks the officer of the watch thinks it his duty to insert.

Memo.-When the foregoing particulars are transferred to the Log-book, they are generally given in fuller detail, and the following record may be of service.

As regards Wind, BEAUFORT's Scale is that generally used; and I have arranged hourly velocity of the wind according to the scale :—

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Weather. Besides defining the character of the winds, there are specialities in the weather which must also be recorded; as

Clear; hazy; cloudy; drizzling rain; foggy; thick fog; gloomy, dark; hail; lightning; misty; overcast; passing showers; squally; heavy squalls; rain; continuous rain; snow; snow squalls; thunder; ugly appearance; direction of the upper clouds; direction of the scud, &c.

Various phenomena are also recorded,-as, waterspouts, icebergs, field ice, &c. The height of the barometer should be inserted at regular intervals, and more frequently when the changes are rapid; also give the height of the thermometer. A swell is recorded in the same way as is the wind, thus a S.W. swell, means a swell from the S.W.

The ship's log should be kept in Civil Time, 24 hours to the day, the first 12 hours being A.M., and the second 12 hours P.M.; by this mode of reckoning, the noon of the Date by Log agrees with the astronomical day, and there can be no confusion in the correction of the elements taken from the Nautical Almanac. The civil day begins at midnight and ends at the midnight following: the astronomical day begins at noon and ends at the noon following: but the noon of any given Date, as May 12, or November 20, is the same in

both methods of reckoning; hence the civil day is 12 hours in advance of the astronomical day.

The barbarism of reckoning by a nautical day, 12 hours in advance of the civil, and 24 hours in advance of the astronomical, day, cannot be too much deprecated, and must have frequently led to errors in the computation of the astronomical data. Besides, two modes of reckoning dates must surely be enough, without the complication of a third, and wholly useless, date.

The LOG-BOOK, headed on each page—

"Journal of the Ship

bound from

towards

is a book ruled like the log-board, in order to contain the daily copies of everything written on the log-board by the officers of the watch as the things occurred; it is written up by the Mate, at noon, and is taken to be the only authentic record of the ship's transactions; the Mate, under the directions of the Master, makes any other notes that circumstances require; and from the Log-Book is deduced the

DEAD RECKONING, which is the Diff. Lat., Dep., and Diff. Long.,—the Lat. in and Long in-and the Course and Dist. made good,-derived from the Courses and Distances made during the 24 hours. The latitude and longitude obtained from the log-board or log-book is written Lat. by D.R. and Long. by D.R.; or Lat. by Acc. (account) and Long. by Acc.-to distinguish them from what is obtained by observation of the sun, &c., which is written Lat. by Obs., and Long. by Obs.

NOTE.-The error in the Distance arising from an error of a quarter of a point in the Course is about one mile in twenty.

MERCATOR'S CHART.

(Refer, when required, to Chart at beginning of the Work.)

If you take a globe and try to find the course and distance between any two places, you will experience considerable difficulty in ascertaining what you require, and you would find it impossible to do so on a map constructed on the globular projection. The early navigators had to contend with this difficulty, and projected what they called the plane chart, on which the parallels and meridians were equidistant straight lines; but the errors in navigation could not have been lessened by the use of such a projection, and this was soon found out. When, however, GERARD KAUFFMAN (better known as MERCATOR) devised the chart which goes by his name, its facilities for the purposes of the mariner were at once recognised, and it is now universally adopted as the only proper chart for general navigation; the parallels and meridians are still straight parallel lines, but only the meridians are equidistant, and the construction is such that the rhumb lines are also represented by straight lines.

You know that the parallels of latitude on the surface of the globe are everywhere equidistant, while the distance between the meridians lessens as we proceed polarwise; and you can at once understand that if, on a plane surface, the parallels are retained equidistant while the meridians are widened out at the poles to the distance they have at the equator, there must be considerable distortion in only one direction, viz., in longitude. But the difficulty in the

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