On the Economy of Machinery and Manufactures - Charles Babbage (interesting books to read in english .TXT) 📗
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straight line. A similar difficulty takes place in figuring
specula for telescopes; the parabola is the surface which
separates the hyperbolic from the elliptic figure, and is the
most difficult to form. If a spindle, not cylindrical at its end,
be pressed into a hole not circular, and kept constantly turning,
there is a tendency in these two bodies so situated to become
conical, or to have circular sections. If a triangular-pointed
piece of iron be worked round in a circular hole the edges will
gradually wear, and it will become conical. These facts, if
they do not explain, at least illustrate the principles on
which the excellence of work formed in the lathe depends.
Of Copying
82. The two last-mentioned sources of excellence in the work
produced by machinery depend on a principle which pervades a very
large portion of all manufactures, and is one upon which the
cheapness of the articles produced seems greatly to depend. The
principle alluded to is that of copying, taken in its most
extensive sense. Almost unlimited pains are, in some instances,
bestowed on the original, from which a series of copies is to be
produced; and the larger the number of these copies, the more
care and pains can the manufacturer afford to lavish upon the
original. It may thus happen, that the instrument or tool
actually producing the work, shall cost five or even ten thousand
times the price of each individual specimen of its power.
As the system of copying is of so much importance, and of
such extensive use in the arts, it will be convenient to classify
a considerable number of those processes in which it is employed.
The following enumeration however is not offered as a complete
list; and the explanations are restricted to the shortest
possible detail which is consistent with a due regard to making
the subject intelligible.
Operations of copying are effected under the following
circumstances:
by printing from cavities by stamping
by printing from surface by punching
by casting with elongation
by moulding with altered dimensions
Of printing from cavities
83. The art of printing, in all its numerous departments, is
essentially an art of copying. Under its two great divisions,
printing from hollow lines, as in copperplate, and printing from
surface, as in block printing, are comprised numerous arts.
84. Copperplate printing. In this instance, the copies are
made by transferring to paper, by means of pressure, a thick ink,
from the hollows and lines cut in the copper. An artist will
sometimes exhaust the labour of one or two years upon engraving a
plate, which will not, in some cases furnish above five hundred
copies in a state of perfection.
85. Engravings on steel. This art is like that of engraving
on copper, except that the number of copies is far less limited.
A banknote engraved as a copperplate, will not give above three
thousand impressions without a sensible deterioration. Two
impressions of a banknote engraved on steel were examined by one
of our most eminent artists,(1*) who found it difficult to
pronounce with any confidence, which was the earliest impression.
One of these was a proof from amongst the first thousand, the
other was taken after between seventy and eighty thousand had
been printed off.
86. Music printing. Music is usually printed from pewter
plates, on which the characters have been impressed by steel
punches. The metal being much softer than copper, is liable to
scratches, which detain a small portion of the ink. This is the
reason of the dirty appearance of printed music. A new process
has recently been invented by Mr Cowper, by which this
inconvenience will be avoided. The improved method, which give
sharpness to the characters, is still an art of copying; but it
is effected by surface printing, nearly in the same manner as
calicoprinting from blocks, to be described hereafter, 96. The
method of printing music from pewter plates, although by far the
most frequently made use of, is not the only one employed, for
music is occasionally printed from stone. Sometimes also it is
printed with moveable type; and occasionally the musical
characters are printed on the paper, and the lines printed
afterwards. Specimens of both these latter modes of
music-printing may be seen in the splendid collection of
impressions from the types of the press of Bodoni at Parma: but
notwithstanding the great care bestowed on the execution of that
work, the perpetual interruption of continuity in the lines,
arising from the use of moveable types, when the characters and
lines are printed at the same time, is apparent.
87. Calico printing from cylinders. Many of the patterns on
printed calicos are copies by printing from copper cylinders
about four or five inches in diameter, on which the desired
pattern has been previously engraved. One portion of the
cylinders is exposed to the ink, whilst an elastic scraper of
very thin steel, by being pressed forcibly against another part,
removes all superfluous ink from the surface previously to its
reaching the cloth. A piece of calico twenty-eight yards in
length rolls through this press, and is printed in four or five
minutes.
88. Printing from perforated sheets of metal, or stencilling.
Very thin brass is sometimes perforated in the form of letters,
usually those of a name; this is placed on any substance which it
is required to mark, and a brush dipped in some paint is passed
over the brass. Those parts which are cut away admit the paint.
and thus a copy of the name appears on the substance below. This
method, which affords rather a coarse copy, is sometimes used for
paper with which rooms are covered, and more especially for the
borders. If a portion be required to match an old pattern, this
is, perhaps the most economical way of producing it.
89. Coloured impressions of leaves upon paper may be made by
a kind of surface printing. Such leaves are chosen as have
considerable inequalities: the elevated parts of these are
covered, by means of an inking ball, with a mixture of some
pigment ground up in linseed oil; the leaf is then placed between
two sheets of paper, and being gently pressed, the impression
from the elevated parts on each side appear on the corresponding
sheets of paper.
90. The beautiful red cotton handkerchiefs dyed at Glasgow
have their pattern given to them by a process similar to
stencilling, except that instead of printing from a pattern, the
reverse operation that of discharging a part of the colour from a
cloth already dyed—is performed. A number of handkerchiefs are
pressed with very great force between two plates of metal, which
are similarly perforated with round or lozenge-shaped holes,
according to the intended pattern. The upper plate of metal is
surrounded by a rim, and a fluid which has the property of
discharging the red dye is poured upon that plate. This liquid
passes through the holes in the metal, and also through the
calico; but, owing to the great pressure opposite all the parts
of the plates not cut away, it does not spread itself beyond the
pattern. After this, the handkerchiefs are washed, and the
pattern of each is a copy of the perforations in the metal-plate
used in the process.
Another mode by which a pattern is formed by discharging
colour from a previously dyed cloth, is to print on it a pattern
with paste; then, passing it into the dying-vat, it comes out
dyed of one uniform colour But the paste has protected the fibres
of the cotton from the action of the dye or mordant; and when the
cloth so dyed is well washed, the paste is dissolved, and leaves
uncoloured all those parts of the cloth to which it was applied.
Printing from surface
91. This second department of printing is of more frequent
application in the arts than that which has just been considered.
92. Printing from wooden blocks. A block of box wood is, in
this instance, the substance out of which the pattern is formed:
the design being sketched upon it, the workman cuts away with
sharp tools every part except the lines to be represented in the
impression. This is exactly the reverse of the process of
engraving on copper, in which every line to be represented is cut
away. The ink, instead of filling the cavities cut in the wood,
is spread upon the surface which remains, and is thence
transferred to the paper.
93. Printing from moveable types. This is the most important
in its influence of all the arts of copying. It possesses a
singular peculiarity, in the immense subdivision of the parts
that form the pattern. After that pattern has furnished thousands
of copies, the same individual elements may be arranged again and
again in other forms, and thus supply multitudes of originals,
from each of which thousands of their copied impressions may
flow. It also possesses this advantage, that woodcuts may be used
along with the letterpress, and impressions taken from both at
the same operation.
94. Printing from stereotype. This mode of producing copies
is very similar to the preceding. There are two modes by which
stereotype plates are produced. In that most generally adopted a
mould is taken in plaster from the moveable types, and in this
the stereotype plate is cast. Another method has been employed in
France: instead of composing the work in moveable type, it was
set up in moveable copper matrices; each matrix being in fact a
piece of copper of the same size as the type, and having the
impression of the letter sunk into its surface instead of
projecting in relief. A stereotype plate may, it is evident, be
obtained at once from this arrangement of matrices. The objection
to the plan is the great expense of keeping so large a collection
of matrices.
As the original composition does not readily admit of change,
stereotype plates can only be applied with advantage to cases
where an extraordinary number of copies are demanded, or where
the work consists of figures, and it is of great importance to
ensure accuracy. Trifling alterations may, however, be made in it
from time to time; and thus mathematical tables may, by the
gradual extirpation of error, at last become perfect. This mode
of producing copies possesses, in common with that by moveable
types, the advantage of admitting the use of woodcuts: the copy
of the woodcut in the stereotype plate being equally perfect.
with that of the moveable type. This union is of considerable
importance, and cannot be accomplished with engravings on copper.
95. Lettering books. The gilt letters on the backs of books
are formed by placing a piece of gold leaf upon the leather, and
pressing upon it brass letters previously heated: these cause the
gold immediately under them to adhere to the leather, whilst the
rest of the metal is easily brushed away. When a great number of
copies of the same volume are to be lettered, it is found to be
cheaper to have a brass pattern cut with the whole of the proper
title: this is placed in a press, and being kept hot, the covers,
each having a small bit of leaf-gold placed in the proper
position, are successively brought under the brass, and stamped.
The lettering at the back of the volume in the reader’s hand was
executed in this manner.
96. Calico printing from blocks. This is a mode of copying,
by surface printing, from the ends of small pieces of copper
wire, of various forms, fixed into a block of wood. They are all
of one uniform height, about the eighth part of an inch above the
surface of the wood, and are arranged by the maker
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