Navigation Instruments

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Which shows you the making of a general Instrument with which to know the hour of the day throughout the world.

The Equinoctial Dial

Now for the making of your standard instruments, you should repair to your usual Ship's Chandler or Instrument Maker. However, there are some instruments that are not as common as they should be, one being the Equinoctial Dial. This Dial is used to know the hour of the day, in all latitudes throughout the whole world, for your compass does not know the hour of the day during Summer, neither in the morning nor evening, neither can you know when the Moon is East or West when she has North declination, as I have shown earlier, and also because your compass stands as flat as your horizon. Wherefore it is good for Mariners to use Equinoctial Dials, for they show the true hour of the day in all latitudes, and also the Moon gives a true Shadow in the Dial in all Latitudes.

The Use of the Moon's Shadow

Now this is useful for many mariners are deceived as to when High tide flows on an East and West Moon, or and point between the Southeast and Northeast, because in setting the Moon with their compass she seems to be East, when she is near the East Southeast in her actual course, and in like manner when the Moon seems West by the compass she shall be a little more than West Southwest in her course. And this is a very perilous matter for those that should put into a tidal channel, harbour or haven knowing that there is enough water if they come in on a full Sea, and then by the error of the compass in reading the Moon's shadow they are deceived.

And when this error is found, many Navigators think that the cause is due to the occasion of some great storm that is likely to follow, whereas this error is caused by no other means than of receiving a false shadow by the Horizontal compass. And this error is especially severe if the Moon is in her greatest declination to the North, that is in the Zodiac signs of the Smith, Thief and Lover, and also the effect is most pronounced if the Dragon's head is three or four Zodiac signs behind the Moon, for then she shall have up to 5 degrees more declination from the Equinoctial than if the Dragon's head be elsewhere, so that if these situations both occur, the Moon will be declined 28 and a half degrees to the North of the Equinoctial.

The Equinoctial Dial Recommended

But to avoid any of these infirmities of readings, I would recommend the use of the Equinoctial Dials. And furthermore I do not think that the Equinoctial dials are used amongst our Mariners here in the Baronies, no matter how good they may be as Navigators, not least because the charge for them is so great, and yet they serve no purpose except to know the hour of the day, and to show the true shadow of the Moon. But not withstanding, I would wish them that are Seafarers to accustom themselves to the dials, for they serve two notable uses, both in coastal journeys and also in long voyages, and to this end I advise that the can be made with a very low charge, for whereas in the Arts of Navigation they are only accepted in brass, they may be made also from wood in the following manner.

The Making of a Wooden Dial

Take a piece of board end at least six inches broad (at your discretion) and half an inch in thickness, then having cut it into a round circle and planed it smooth, you may either engrave in it the 32 points of the compass, or else paint them upon it with some colours, with the 24 hours also upon both sides, as shown in this figure:

That done, take a wire of exactly the diameter of the Instrument and pierce it through the exact centre of the Instrument, than make it fast so that one end be halfway through on one side, and the other half on the other side; this done, make a frame with three pieces of board end to hang the Instrument or Dial from, with one upright board attached by a pin on the East point, and another on the West point, and the third board serving as a level base between the uprights. Then take another board end, being square, and with a pair of compasses draw a quarter circle of exactly the size of the quarter of the dial, and cut all that away; and then the inner curve on the rest of the square is to be divided into 90 equal parts, marking it thus: 0, 10, 20, 30, 40, 50, 60, 70, 80, 90. Last of all, let this board be placed in the middle of the frame in parallel to the uprights, so that the mark 90 may stand right under the very middle of the dial, and there made fast. This board should be in such a position that the very end of the wire runs up to the hollow curve howsoever the dial be tilted on its pins, and so it is finished, and will stand altogether in this form.

The Use of an Equinoctial Dial

The use of this Dial is most necessary in a ship, as you oft have occasions to transport yourselves into all manner of climates. And to know the true hour of the day do this: set the Dial to point North-South by your compass with the curved degrees to the South, and then set the end of the wire right against that degree which is your Latitude, and then other end of the wire will point just to the Pole. Then look what shadow the wire gives by the sun against the sloping dial; that is the true hour of the day. In like manner you may know the true hour of the night by the Moon's shadow, and also where the Moon's shadow falls is its true bearing.