Mathematical Instruments.
14. Having had some perusal of Books of Astronomy and Geography; I had the good Fortune as to find some Mathematical Instruments, which formerly I was ignorant of, which I shall set down in this place, to which may be added those mentioned in the succeeding chap.9. numb.46. 47. &c.
Hour circle and index
CLXVI. In this square, in the dexter chief is placed an appurtenance of the Globe, whether Celestial or
Terrestial, without which there can be no right Judgment
be given of several things; It is by all or most Artists
nominated or called the Hour Circle and its Index;
it is a small Brasen Circle, fixed on the Meridian of the
Globe, whose Center is the Pole of the World; it is divided into 24 halfs and quarters, which in the
Revolution of the Globe are all pointed at with an
Index, which to that purpose is fixed on the Axis of
the Globe. The use of this Hour Circle, is for shewing
the time of the several Mutations and Configurations
of Celestial appearances.
Globe's quadrant of altitude
In the Base of this square, is the Globes Quadrant
of Altitude, it is a thin long Brass Plate divided into 90
degrees, and marked upwards with 10, 20, 30, &c. to
90. It is Rivetted to a Brass Nut, which is fitted to the
Meridian of the Globe, and hath a screw in it to screw
on any degree of the Meridian: When it is used, it is
screwed to the Zenith; its use is for measuring the Altitudes,
finding Amplitudes and Azimuths, and describing Almicantaraths.
Quadrant with moving index
In the Sinister chief is another sort of Quadrant,
with a Moving Index; they are generally made of
hard Wood, as Box, but the best are of Brass, whose
use is to find the Altitude of either Sun, Moon, or
any Star, by holding the lower side Parallel to the Horizon, and moving the Index till the Object be seen
through the holes or slits of the sight placed on the
Index, and where it falls then on the Figure of the
Limb, that is the elevation required.
Related text(s) Quadrant parts
Astrolabe
CLXVII. He beareth an Astrolobe.
This is a round Instrument made of Brass, with a Level and Perpendicular
pieces fixed in the middle thereof, wherein is a Center
with a moveable Label or Ruler, whereon is placed
two Sights; upon one of the flat or plain sides of the
Circle is described or divided into 360 equal part or
degrees, 6 in each quarter; upon the Perpendicular, on
the out-side the Circle is fastned an eye with a Ring in,
by which the Instrument hangs, with the line of Level
parallel to the Horizon: The use is to take Altitudes or
Heights, by moving the Label so that the Sun Beams
may pierce through the upper and nethermost Vane or
Sight at one time, and where the points of the Label
lies on, is the degree and part of the degree that the
Sun is high above the Horizon. The further use of this
Instrument is set forth at large by Mr Wright, in his
division of the whole Art of Navigation, annexed to his
Correction of Errours.
Related text(s) Astrolobe parts
Hoop dial
CLXVIII. In this square is the shape of two Sun Dials, which are generally cast in Brass.
The first is called an Hoop, or Circle Dial; it hath
the hours of the Day made within the Hoop, and on
the out side the days of the Month, and the Months,
with an Eye and Ring to hang it by, which are moveable, and will be set to any day of the Month, where
the hole for the Sun to shine through, being placed, the
Sun will cast a Light through it upon the Figure, which
is the absolute Hour of the day.
Horizontal sundial
The second is called an Horizontal Sun Dial; it
is made of Brass after the manner in all respects to the
aforesaid Hoop Dial; with this addition to it, of a Meridian or Horizontal line of Brass fixt in the middle of
the Hoop from one side to the other, in the Center
whereof is set a moveable Needle, like the Needle of
a Mariners Compass.
Jacobs Staff
CLIX. In this square are some Geometrical Instruments which are to be transmitted to the next
chapter, as
First in the dexter Chief is another form of a Jacob
Staffe, This is an Instrument, diversly made, them
only and chiefly made, doth consist of a Staff about a
yard long and about an Inch square, upon it is fitted a
Vane, (or sometimes two or three) so as it may slide
pretty stiff upon the staff, and stand at any of the divisions it is set too. The use of it is for the taking of Altitudes,
which is done by putting the end of the cross-staff
(which is next 90 degrees) to your cheek, upon the outer corner of your eye, and holding it there steddy with
your right hand, and with your left, you must move
the Vane, or Cross peece, till you see the Horizon ioyned or Level with the lower end thereof, and the Sun or
Star with the higher end; Then the degree and part of
the degree, which the Vane cutteth upon the Staffe, is the
height of the Sun or Star. Se chap.9. numb.48.
Clock's balance wheel
The Second in the dexter base, is termed the Ballance Wheel of a Clock, this is the Primum mobile,
the first moveing wheel by which all the others are set
on going; If it stand, the Clock is silent. Some call it
the Wauch Wheel, or Motion Wheel.
Paralaligreme
The third is an Instrument used for Draft, or drawing; and is termed a Paralaligreme: by the several
motions, and moveing of the Pins of this Instrument,
and the observations of its station; it will do several
kinds of works in drawing of Figures: either bigger
then the patern, as big as the patern, or less then
the patern, to what degrees in each (as bigger or lesser) as the Workman pleaseth. It hath several parts
which I shall name onely.
Semi circle instrument
In the Sinister chiefe is a Semi Circle Instrument, with a Plumet and Line fixed to it, with
this, as well as with the Quadrant, Levels Heights
Depth and distances of places are taken and known; of
which See more chap.9. numb.46. 47. This is also
called a Geometrical, or Mathematical Semi-Circular
Instrument.
Related text(s) Paralaligreme parts
Rule
[The following images are not included on the plate and lack descriptive text
but seem to relate to the preceding ones in section 14]
Clinatory
Circle with sights
[This instrument is drawn on the draft version of Chapter 8b, square 164, but has been replaced on the printed version.]
Previous section
