1872.-February 1st.-Find the times of high water A.M. and P. M. at

Stromness.

Open the tide tables at page 106 and see the constant and port of reference for Stromness. Constant + 0h. 32m. Port of reference, Thurso.

Now, turn over for February and seek Thurso, the port of reference. Having found Thurso in the month of February, write down the Morning and Afternoon tides given on the date required.

Port of reference, Thurso, Oh. 23m. Morning.

Oh. 45m. Afternoon. + 0 32

1 17 P.M.

1872.-February 1st.-Required the times of high water A. M. and P. M. at Dundee.

Open the tide tables, page 106, and seek Dundee. Note the constant and port of reference. Constant Oh. 50m. Port of reference, Sunder

land.

Now, turn up for February and find the port of reference, Sunderland, and write down the Morning and Afternoon tides for the 1st, the date required.

Port of Reference, Sunderland, 7h. 33m. Morn.

7h. 55m. Afternoon.

1. 1872. February 2nd.-A.M. and P.M. tides at Stromness. 2. 1872. February 2nd.-A.M. and P.M. tides at Dundee. 3. 1872. February 3rd.-A.M. and P.M. tides at Lerwick. 4. 1872. February 1st.-A.M. and P.M. tides at Aberdeen. 5. 1872. February 1st.-A.M. and P.M. tides at Dunbar. 6. 1872. February 9th.-A.M. and P.M. tides at Filey Bay.

ERROR OF COMPASS BY AMPLITUDE.

P.M. AT SHIP.-If the apparent ship time is P.M. make no alteration, but write down the time as stated in the example, with the day at the head of the example before it.

A.M. AT SHIP.-If the time is A.M. make the date one day less, and add 12 to the hours.

FIND THE GREENWICH DATE.-To the App. Ship time apply the Long. in time from Table 19, or multiplying the Longitude by 4 and dividing by 60:

West, adding;

East, subtracting.

If the Long. in time, West, added to the ship's time, exceed 24 hours, subtract 24 from the hours, and make the date one day more.

If the Long. in time, East, to be subtracted, is greater than the ship's time, add 24 to the hours of the ship's time, and make the date one day less.

TO CORRECT THE DECLINATION.-Take out the Decl. from page 1 for the Greenwich date, and put the Decl. for the following day under it.

If the Declinations are of the same name, subtract the less from the greater; but if contrary names add them together, and name the result Daily Variation.

Under the Daily Variation write the hours and minutes of the Greenwich date, and take out the Log. of each from Table 33. These two Logs. added together give the Log. of the correction for Declination found in the same Table.

If the Decl. is INCREASING, ADD the correction to; but

If the Decl. is decreasing, subtract the correction from the Declination for the Greenwich date.

Note.-When the Decls. are of contrary names the Decl. is decreasing. In such a case, if the correction to be subtracted is greater than the Decl., subtract the Decl. from the correction and name the result contrary to the Decl.

TO CORRECT THE DECL. BY HOURLY DIFFERENCE.-Take out the Decl. from page 1 of the month for the Greenwich date and also the "Diff for 1 hour" from abreast of the Decl. Multiply the "Diff for 1 hour" by the hours and tenths of an hour of the Greenwich date.

Decl. increasing, add;

Decl. decreasing, subtract the correction.

TO FIND THE TRUE AMPLITUDE.-To the log. secant of the Latitude (10 subtracted from the index), add the log. sine of corrected Declination; the sum will be the log. sine of the true amplitude; Logs. from Table 25.

TO NAME THE TRUE AMPLITUDE.-Name it from the East if A.M; and from the West if P.M. Towards the North if Decl. is North; but towards the South if Decl. is South.

TO FIND THE ERROR.-Under the true amplitude, put the compass amplitude as given in the example. Amplitudes contrary names (one N. and the other S.) add them together; same name, subtract the less from the greater.

TO NAME THE ERROR.-The observer must suppose himself at the centre of the compass looking towards the point from which the amplitudes are reckoned; then, if the true amplitude is to the right of the compass amplitude the error is East; but, if the true is to the left of the compass the error is West.

Declination Nothing.-If the corrected Decl. is nothing or less than 30 seconds, the true amp. is nothing: that is, E. 0° 0' if A.M.; but W. 0° 0' if P.M. at ship.

Latitude Nothing.—When the Lat. is nothing, the Corrected Decl. is the true amp.

Note. When either the Decl. or Lat. is nothing, no logs. are required.

TO FIND THE DEVIATION.-Under the Error of the Compass place the Variation, and subtract if of the same name; but add if contrary names.

TO NAME THE DEVIATION.

When the Error and Variation are contrary names, name the Dev. the same as the Error.

When the Error and Variation are the same name; mark the Dev. the same as the Error if the Error is the greater, but the contrary name if the Variation is the greater.

When the Error is nothing, the Deviation is the same as the Variation, but of a contrary name.

When the Variation is nothing, the Deviation is the same as the Error, of the same name.

ANOTHER METHOD TO FIND AND NAME THE DEVIATION.Place the variation under the error of the Compass, and suppose the variation to be of a Contrary name to what it is given; that is, if it is East suppose it West, and then find the deviation the same as the Longitude in is found at the end of the Day's Work.

1874. October 2nd, at 6h. 16m., P.M., Apparent Ship time; in lat. 44° 38'; long. 20° W. The sun's amplitude by compass W. 10° 30' S.

Find the error of the compass.

1874.-March 29th, at 6h 20m. A. M., Apparent time at ship; in lat. 49° 30′, long. 156° E. The sun's amplitude by compass E. 3° S. Find the error of compass.

d. h. m.

Ship App. T. March 28 18 20 Long. 156° E. Decl. 28th 3° 2′ 17′′

N.

Long. in time...

Table 33.

1874. June 3rd, at 3h. 54m. A.M., App. T. Ship; in lat. 50° 50′; long. 168° 15′ W. Sun's amp. by compass E. 39° 30′ N. Find the true amp. and error of compass; and supposing the Variation to be 13° E.: find the Deviation.