Copyright Dr. Elizabeth Garner and Gary Hind June 1, 2014

CLOSEUP of the courier tube lower left corner wind rose map
CLOSEUP of the courier tube lower left corner wind rose map

Today were are going to look at one of the new encodings that have been found in Melencolia, the number of which is becoming astounding. If we take a very close look at the face cover of the secret courier tube in the lower left hand corner of Melencolia, we find that the cover is actually a depiction of a navigational tool or map known  as an astrolabe, a nautical tool.  Here is an example of an astrolabe

Basic depiction of an astrolabe

You can see that the one depicted on the courier tube is more simplified. Astrolabes are used to show how the sky looks at a specific place at a given time. This is done by drawing the sky on the face of the astrolabe and marking it so positions in the sky are easy to find. To use an astrolabe, you adjust the moveable components  to a specific date and time. Once set, much of the sky, both visible and invisible, is represented on the face of the instrument. This allows a great many astronomical problems to be solved in a very visual way. Typical uses of the astrolabe include finding the time during the day or night, finding the time of a celestial event such as sunrise or sunset and as a handy reference of celestial positions. Astrolabes were also one of the basic astronomy education tools in the late Middle Ages. Old instruments were also used for astrological purposes. The typical astrolabe was not a navigational instrument although an instrument called the mariner’s astrolabe was widely used in the Renaissance. The mariner’s astrolabe is simply a ring marked in degrees for measuring celestial altitudes. The one depicted on the face of the courier tube is a mariner’s astrolabe. Here’s one example of how this tool was used.

One type was known as a compass rose which is on the tope of the courier tube

Finding the time of day

The time of day is found in the following steps:

  1. The altitude of the Sun or a bright star is determined using the back of the instrument. The astrolabe is held above eye level from the suspension. The astrolabe is oriented so the Sun or star is lined up with the back of the astrolabe. The alidade is rotated until the Sun’s shadow or the star itself is visible through the sights on the alidade. The altitude is noted from the altitude scale on the back of the instrument.
  2. The Sun’s position on the ecliptic is found by setting the alidade on the date and reading the Sun’s longitude on the zodiac scale.
  3. On the front of the astrolabe, the rule is rotated until is crosses the ecliptic at the Sun’s current longitude. The point where the rule crosses the ecliptic is the Sun’s current position.
  4. The rete and rule are rotated together until the Sun or star pointer is at the measured altitude.
  5. The rule points to the apparent solar time on the limb. Apparent solar time is the time as shown on a sundial and is different for each longitude. In modern use, apparent solar time must be corrected to zone time by compensating for the equation of time and the difference in longitude from the center of the time zone.

The part called the rule has to be magnetized.

One of the earliest man-made navigation tools was the mariner’s compass, an early form of the magnetic compass(c.13th Century). Initially used only when the weather obscured the sun or the North Star, these first compasses were very crude. The navigator would rub an iron needle against a lodestone, stick it in a piece of straw and float it in a bowl of water. The needle would point in a northerly direction”

We don’t immediately see anything that looks like a rule on this astrolabe.  But if we look on the hammer we find a nail near the polyhedron.

Nail for the Compass Rose map for magnetization
Nail for the Compass Rose map for magnetization

It is a well known fact that metal objects can be magnetized simply by hitting them with a hammer several times. A pin for example can be magnetized by hitting one end of the object while it is facing NORTH-SOUTH. More accuracy at this point would gain stronger magnetism and if placed though a straw or on a thin piece of paper – floating in a bowl of water – it would spin and align itself to point NORTH – SOUTH.

The hitting action of the hammer agitates the electrons inside the pin’s metal structure and as they spin they realign themselves into the earth’s magnetic force field.

Another way of magnetizing metal is by rubbing it against a lodestone {magnetite) this method was used by medieval sea farer’s, after using a lodestone to magnetize a thin piece of metal wire it would be pivoted onto a vertical balance pin, a compass card (wind rose) which depicts all the cardinal points and intersections would be placed underneath the needle, this would show the direction they were travelling in and which winds to use.


And so we have the parts to use this compass to locate places on the earth.

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