farthest from you without moving, or altering
the Label from the Horizontal Line; then look
again, and if you can see the same Point as before
through the two sights, 'tis a sign the Horizontal
Line of your Astrolabe is parallel to the Hori∣zon.
The Lines drawn from the Center of the
Astrolabe, divide the Circumference of the
Heavens in the same manner as it divides the
Circumference of the Astrolabe; for all Circles that [ 10]
have the same Center, are divided in the same
manner, by the Lines drawn from the common
Center.
This Instrument is divided into as many equal
parts as the Heavens, viz. 360 Degrees, how∣ever
a quarter part is sufficient.
The use of this Instrument is easy, there be∣ing
no more than to hold it so with your left
Thumb through the Ring, that it may have a free
Motion, so that the Horizontal Line may be [ 20]
parallel to the Horizon; then turn your right
Side, and the Graduated part of the Astrolabe
so to the Sun, that the Sun shine neither on the
one, nor the other side: Then lift up the Label
with your right Hand, until the Sun Beams en∣tring
through the Hole in the lower Sight, and
the Label will shew the Suns Altitude above the
Horizon. And if you count from the Horizon∣tal
Line to the Label, from the Zenith to the
Label, it will be the distance of the Sun from [ 30]
the Zenith. But be sure that the Astrolabe doth
hang upright, otherwise you will be at a great
loss.
It is also covenient to know the true Meridian
at Sea, for Sayling far East, or West, the Com∣pass
varieth; therefore to know the same, do
thus: Set the Sun with your Compass at its
rising above the Horizon, and then (knowing
what Part and Point the Sun riseth at) set the
Sun with the Compass at the departing under the
Horizon, which being found out, you shall under∣stand [ 40]
whether the Compass be varied, and how
much, by the dividing the Piece of the Circle, con∣tayned
between the rising and setting of the Sun, in∣to
two equal parts; for the right Line drawn from
the Center of the Fly through the Point of the
partition, expresses the true Meridian, and the
proportion of the Circle contained between the
said Line, and the South Point of the Compass
shews the quantity of the Variation.
The QVADRANT is an Instrument that [ 50]
contains the 4th part of a Circle, which is 90 De∣grees,
and represents the distance between the
Horizon and the Zenith. This Instrument is of
much use upon Land, whereby many Observati∣ons
are performed, but is now not much used at
Sea; The Figure of the Quadrant is made use of
in the Treatise of Geometry, and therefore omit∣ted
here.
The SEA-CHART, or MERCATORS [ 60]
CHART, is an Instrument by which the
Mariner guids the Ship, from place to place, by
such Courses as by the Chart are laid down;
and for the understanding thereof observe these
or the like Directions; First, That the Latitudes
of such places as are within the Chart, be well
known according as they are exprest in the said
Chart. Secondly, That the Countreys, or Georgra∣phy
of the Chart, be known, with the Capes,
Bays, Promontories, Havens, Ports, Rocks, Sands
and the like. Thirdly, That you understand to
measure the distances of places upon the Chart.
Fourthly, That the Line drawn upon the Chart
with their several properties, be likewise known;
And Fifthly, That by this Chart you may under∣stand
the true Courses between any Capes, Isles,
Continents, or the like.
This Chart is better to be bought, as other
Instruments, which is a very large, white,
and smooth skin of Velom or Parchment; Upon
this first describe a Square; then divide the
Aequinoctial Line into as may equal Parts or
Degrees, as you have occasion for; Then draw
on your Degrees of Latitude, then your Paral∣lels
through every 5th or 10th Degree of the
Meridian, and the Meridians through every 5th
or 10th Degree of the Aequinoctial. As for the
Rhumbs, Capes, Harbours, Rocks, Isles, &c. to
be described thereon, must be placed according to
their true Latitude, and Longitude.
The Latitude of places by the Chart, is
thus found out; upon the place whose Latitude
you desire to know, set one Foot of your Com∣passes;
then stretch the other Foot to the next
East, or West Line, for that Line is your directi∣on,
keeping that Foot still upon the same Line,
moving your Hand and Compasses to the Gradua∣ted
Meridian, and there that Foot of the Com∣pass
which stood upon the place, whose Lati∣tude
you would know, shews the Latitude of
the same place.
'Tis not material to give a Draught of the
Sea-Chart, these Instructions being sufficient;
but if not, any Instrument-Maker of whom you
buy on, will soon shew the use, with directions
to use it, as indeed of any other.
I shall omit the Plain Chart as being much of
the same nature, but not so true.
The SENICAL QVADRANT is
composed of Concentrick Arches, or rather Quar∣ters
of Circles, and of three sorts of right Lines.
First, Those Parallel to the Line shews the Sines,
and Meridians, and are Parallel to the North and
South, upon which the Leagues of Latitude are
counted. Secondly, Those drawn Parallel to the
Line, give the Sines, Complements, and Paral∣lels;
and are Parallels to the East and West, up∣on
which the Leagues of Longitude, or depar∣ture
from the Meridian are reckoned; and
Thirdly, Those drawn from the Center of the
Quadrant, to the Limb, shew the Rhumbs of the
Compass, or the several Courses; and upon them
the Distance, or Leagues Sailed are reckoned,
which said Leagues are marked by the several
Arches, or Quarters of Circles.
Observe, that when the Distances are great,
every Arch or Line cannot be reckoned for a
League, as when the Distances are small; so that
in such Case you may reckon them for what
you please, as your occasions require, that is,
either, 2, 3, 4 or more Leagues; and the Arches
must also be reckoned for as much as you
have reckoned the Lines of Latitude, and Lon∣gitude;
for Example, If you reckon an Arch for