DOI Page / Citation link:
https://doi.org/10.11588/diglit.19574#0220
P I A 203
and, when the fun {nines upon the glafs at the nodus, its beams
will reflect upon the hour of the day.
Some helps to a young dialtft, for his more orderly and quick making
of Dials. See plate V, fig. 2.
It may prove fomething difficult, to thofe that are unpraclifed
in mathematical projections, to divide a circle into 360 degrees,
or, which is all one, a femicircle into 1.80, or a quadrant into
90 degrees.
The fpeedieft way of doing which is by a line of chords,
which, if you will be curious in your practice, you may make
yourfelf; or, if you account it not worth your while, you may
buy it already made on box or brafs, of molt mathematical in-
ftrument makers.
This inftrument they call a plain fcale, which does not only
accommodate you with the divifions of a quadrant, but alfo
ferves for a ruler to draw ftraight lines with.
The manner of making it is as follows:
Defcribe upon a fmooth, flat, even-grained board a quarter of
an whole circle, as b c, whofe radius a 1j, or ac, may be
four inches, if you intend to make large Dials; or two inches, if
fmall; but, if you will, you may have feveral lines of chords on
your fcale or rule.
Divide this quadrant into ninety equal parts, as you are taught
in the making the horizontal Dial.
Then draw clofe by the edge of your ftraight ruler a line pa-
rallel to the edge, and at about one twentieth part of an inch a
fecond line parallel to that, and at about one eighth of an inch a
third line parallel to both.
Then place one foot of your compafles at the beginning of the
firft degree on the quadrant defcribed, on the board, as at b,
and open the other foot to the end of the firft degree, and tranf-
fer that diftance upon your rule, from b to the firft mark or di-
vifion, between the two firft drawn lines.
Then place one foot of your compafTes again at the begin*
ning of the firft degree on the quadrant defcribed, on the board,
as at b, and open the other foot to the end of the fecond degree,
and transfer that diftance upon your rule, from b to the fecond
mark or divifion, betv/een the two firft drawn lines ; and thus
meafure the diftance of every degree from the firft degree de-
fcribed on the quadrant, and transfer it to the rule.
But, for diftincYton fake, you may draw every tenth divifion
from the firft line parallel to the edge of the third line, and mark
them in fucceffion from the beginning with 10, 20, 30, to 90;
and the fifth divifions you may draw half way, between the fe-
cond and third parallel lines ; the fingle divifions only between
the two firft parallel lines. So is your line of chords made.
The
and, when the fun {nines upon the glafs at the nodus, its beams
will reflect upon the hour of the day.
Some helps to a young dialtft, for his more orderly and quick making
of Dials. See plate V, fig. 2.
It may prove fomething difficult, to thofe that are unpraclifed
in mathematical projections, to divide a circle into 360 degrees,
or, which is all one, a femicircle into 1.80, or a quadrant into
90 degrees.
The fpeedieft way of doing which is by a line of chords,
which, if you will be curious in your practice, you may make
yourfelf; or, if you account it not worth your while, you may
buy it already made on box or brafs, of molt mathematical in-
ftrument makers.
This inftrument they call a plain fcale, which does not only
accommodate you with the divifions of a quadrant, but alfo
ferves for a ruler to draw ftraight lines with.
The manner of making it is as follows:
Defcribe upon a fmooth, flat, even-grained board a quarter of
an whole circle, as b c, whofe radius a 1j, or ac, may be
four inches, if you intend to make large Dials; or two inches, if
fmall; but, if you will, you may have feveral lines of chords on
your fcale or rule.
Divide this quadrant into ninety equal parts, as you are taught
in the making the horizontal Dial.
Then draw clofe by the edge of your ftraight ruler a line pa-
rallel to the edge, and at about one twentieth part of an inch a
fecond line parallel to that, and at about one eighth of an inch a
third line parallel to both.
Then place one foot of your compafles at the beginning of the
firft degree on the quadrant defcribed, on the board, as at b,
and open the other foot to the end of the firft degree, and tranf-
fer that diftance upon your rule, from b to the firft mark or di-
vifion, between the two firft drawn lines.
Then place one foot of your compafTes again at the begin*
ning of the firft degree on the quadrant defcribed, on the board,
as at b, and open the other foot to the end of the fecond degree,
and transfer that diftance upon your rule, from b to the fecond
mark or divifion, betv/een the two firft drawn lines ; and thus
meafure the diftance of every degree from the firft degree de-
fcribed on the quadrant, and transfer it to the rule.
But, for diftincYton fake, you may draw every tenth divifion
from the firft line parallel to the edge of the third line, and mark
them in fucceffion from the beginning with 10, 20, 30, to 90;
and the fifth divifions you may draw half way, between the fe-
cond and third parallel lines ; the fingle divifions only between
the two firft parallel lines. So is your line of chords made.
The