> Check out Epact for some examples. http://www.mhs.ox.ac.uk/epact
Expanding on my earlier post, I'd like to discuss some of the nautical
tools a sea captain may have used or carried:
As I said before, the compendium was a collection of miniature tools in one
piece. Sort of a "Leatherman" or "Swiss Army Knife" approach to
many of these tools are labelled astronomical, but the simple fact is that
the small size made them pretty much useless for anything but the most
diffident astronomical observation. this is because the resolution of the
measurements obtained therefrom cannot be all too accurate. As a point of
comparison, Tycho Brahe had a quadrant on his roof that he used that was 12
feet in radius, and has scales that measured to a very fine precision.
seconds of a degree.
A pocket compendium, could by comparison get you reliably within a degree
That is plenty close enough for navigation, though. So I'd expect that most
of these are travellers compendia (it's use would not have been limited to
the sea, but surveyors, explorers and caravan traders would have deeded to
find and determine latitude, as well, and been similarly restricted in the
amount of baggage they could carry)
Some compendia from the middle 1500's for your reference:
You will note that the mariner's astrolabe is constructed in a
fundamentally different method from the astronomical astrolabe which is
usually made utilizing a large thin plate for the "mater".
here is an example of an astronomical astrolabe, for comparison sake:
This difference in construction is mainly due to the fact that the purpose
of the mariners astrolabe was limited to finding elevation of celestial
objects, as opposed to an astronomical astrolabe which primarily tracked
the position of important stars in the sky, and served as a calendar as
well as a calculator of sorts. They often had several latitude plates that
were each designed to present a celestial coordinate system relevant to
different latitudes, on which a "rete" carrying the positions of the stars
turned. the use of a rule and alidade to find elevation was secondary, and
sometimes left off entirely.
The rete and plate feature is only effective when you already KNOW the
latitude, which a rooftop astronomer like Tycho Brahe would be well aware.
The Mariners Astrolabe consistend ONLY of a rule and astrolabe and was was
used to FIND the latitude.
The Mariners astrolabe's use aboard a ship necessitated a larger and
heavier construction to damp the effect of the deck's roll and pitch, and
the cut out centers present less wind resistance, this and the heavier
construction allow it to hang pretty much vertically in all but extreme
other instruments you may have used:
Basically used geometry to calculate the angle between the horizon and the
Could also be used to triangulate distance from two known points. If you
know the distance between them, you can determine your distance from them
by the angle you capture between them.
Basically a sort of half astrolabe/half quadrant. Often small enough to
wear as a pendant.. hardly ever more than 4 inches across. The two ends are
lighted to line up and the resultant angle is read off the scale.
The most basic astronomical tool, you sight along one edge, and read the
angle from the pendant weighted string's position on the scale.
The also often included tools for calculation, such as a Shadow square,
which was a geometrical right angle incised with proportional marking so
that a simple calculation of those markings could yield valuable
information such as height or distance of an observed object, etc.
Lead and Line - finding the depth of the water:
(note: I have not yet found examples of the use of the specific flags at
specific depths, as outlined at this site, attested to in period
documentation. It is clear from the records that the lead and line was used
at all hours, so some strictly tactile method of reading the depth would
certainly have been useful when sounding at night. But what method that was
in period is unknown to me.)
Chip log - finding the speed of the ship
Watch glass - tracking time
Traverse board - tracking course and speed
- the traverse board was pegged at each ringing of the watch bell (half
hour intervals) with the speed and direction of the ship. at the end of
each watch the officer of the watch would take the readings down and clear
the board for the next watch. this allowed the navigator to make a dead
reckoning of his position.
Hope I have helped you.