DOI Seite / Zitierlink:
https://doi.org/10.11588/diglit.20658#0025
OF DRAWING.
The parallel rule is an instrument used for drawing parallel and perpendicular lines, and is often
necessary in every species of mathematical drawing on account of its facility and ease.
There are several instruments invented under this name ; some to answer particular purposes)
and others for more general use. The most common consists of two straight rules, connected
together by two equal and parallel brass bars, which move freely about the rivets by which they
are fastened to the rules, and thereby always maintain the two rules in a parallel position, at
whatever distance they may be set from each other. The modern, and more improved ones, are
of a more complex construction; they are also more general in their uses than the former : a
very good one is that invented by Mr. Haywood, by some called the protracting parallel rule,
delineated in Plate I. Its general use will appear evident from inspection. Each of the rules-,
m and n, turns upon a center, whereby it may also be made subservient for the laying down
of angles; and besides its use as a parallel rule it forms the best kind of callipers or gauge, and
answers all the purposes of a square or bevel; and by means of its sliding in a groove, the two
rules, m and n, may be set to any parallel distance from each other. In a word, its uses are too
numerous to be mentioned here.
The small hair compasses have a round head like that of the bow compasses, and are very
convenient for striking small circles, or taking small extents with accuracy.
The pentograph is the most useful of any instrument hitherto invented, for copying any kind
of drawing, which it does very correctly ; either of the same size with the original., or of a less
or greater size ; at the pleasure of the draftsman.
It is usually made of four fiat rules of wood or brass ; the two longer joined together at the
end a, by a double pivot, which is fixed to one rule, and works in two small holes placed at the
end of the other rule: the two shorter rules are also joined together at their ends g ; and joined
to the middle of the longer rules of e and h, by similar pivots-. Under each joint is an ivory
castor to support the instrument, and enable it to move in every direction with freedom. There
is a sliding box, b, fixed on one of the longer rules, and a similar box., d, on. one of the shorter
rules: each box is furnished with a cylindric tube, to carry either the tracing point, crayon, or
fulcrum, and also with a milled nut, by which they may be fixed, at any part of the rule, k is a
leaden weight called the fulcrum, enclosed in a mahogany box, which may be considered as the
center of the instrument, and about which the instrument moves when in use. Two of the rules
are graduated with two scales each ; and the fiducial edges of the boxes b and d are set to these
scales according to the size of the work to be drawn.
The crayon, tracer, and fulcrum must always be in a right line, and should be so proved by a
string stretched over them. If they do not coincide with the right line, there is an error either
in fixing the sliding boxes, or in the graduation of the instrument. There is generally a string
extended from the tube which holds the pencil or crayon through the three small knobs e a h, to
the tracing point c : and by pulling which, the pencil or crayon is occasionally lifted up, to
prevent making any false or imperfect strokes.
It is evident, from an inspection of this instrument, that as the tracer c moves over the lines
of the original piece, the pencil in the box b will describe similar lines on the paper; the whole
instrument moving in every part, except where it rests on the fulcrum k.
To copy a plan or drawing exactly of the same size with the original. In this case, the sliding
boxes b and d are to be set to the division marked 12 on the rules; then the crayon or black-lead
pencil being put into the box b, the tracing point fixed at c, and the box d placed upon the ful-
crum
The parallel rule is an instrument used for drawing parallel and perpendicular lines, and is often
necessary in every species of mathematical drawing on account of its facility and ease.
There are several instruments invented under this name ; some to answer particular purposes)
and others for more general use. The most common consists of two straight rules, connected
together by two equal and parallel brass bars, which move freely about the rivets by which they
are fastened to the rules, and thereby always maintain the two rules in a parallel position, at
whatever distance they may be set from each other. The modern, and more improved ones, are
of a more complex construction; they are also more general in their uses than the former : a
very good one is that invented by Mr. Haywood, by some called the protracting parallel rule,
delineated in Plate I. Its general use will appear evident from inspection. Each of the rules-,
m and n, turns upon a center, whereby it may also be made subservient for the laying down
of angles; and besides its use as a parallel rule it forms the best kind of callipers or gauge, and
answers all the purposes of a square or bevel; and by means of its sliding in a groove, the two
rules, m and n, may be set to any parallel distance from each other. In a word, its uses are too
numerous to be mentioned here.
The small hair compasses have a round head like that of the bow compasses, and are very
convenient for striking small circles, or taking small extents with accuracy.
The pentograph is the most useful of any instrument hitherto invented, for copying any kind
of drawing, which it does very correctly ; either of the same size with the original., or of a less
or greater size ; at the pleasure of the draftsman.
It is usually made of four fiat rules of wood or brass ; the two longer joined together at the
end a, by a double pivot, which is fixed to one rule, and works in two small holes placed at the
end of the other rule: the two shorter rules are also joined together at their ends g ; and joined
to the middle of the longer rules of e and h, by similar pivots-. Under each joint is an ivory
castor to support the instrument, and enable it to move in every direction with freedom. There
is a sliding box, b, fixed on one of the longer rules, and a similar box., d, on. one of the shorter
rules: each box is furnished with a cylindric tube, to carry either the tracing point, crayon, or
fulcrum, and also with a milled nut, by which they may be fixed, at any part of the rule, k is a
leaden weight called the fulcrum, enclosed in a mahogany box, which may be considered as the
center of the instrument, and about which the instrument moves when in use. Two of the rules
are graduated with two scales each ; and the fiducial edges of the boxes b and d are set to these
scales according to the size of the work to be drawn.
The crayon, tracer, and fulcrum must always be in a right line, and should be so proved by a
string stretched over them. If they do not coincide with the right line, there is an error either
in fixing the sliding boxes, or in the graduation of the instrument. There is generally a string
extended from the tube which holds the pencil or crayon through the three small knobs e a h, to
the tracing point c : and by pulling which, the pencil or crayon is occasionally lifted up, to
prevent making any false or imperfect strokes.
It is evident, from an inspection of this instrument, that as the tracer c moves over the lines
of the original piece, the pencil in the box b will describe similar lines on the paper; the whole
instrument moving in every part, except where it rests on the fulcrum k.
To copy a plan or drawing exactly of the same size with the original. In this case, the sliding
boxes b and d are to be set to the division marked 12 on the rules; then the crayon or black-lead
pencil being put into the box b, the tracing point fixed at c, and the box d placed upon the ful-
crum