CHAPTER 27.

On Contriving Machinery

318. The power of inventing mechanical contrivances, and of
combining machinery, does not appear, if we may judge from the
frequency of its occurrence, to be a difficult or a rare gift. Of
the vast multitude of inventions which have been produced almost
daily for a series of years, a large part has failed from the
imperfect nature of the first trials; whilst a still larger
portion, which had escaped the mechanical difficulties, failed
only because the economy of their operations was not sufficiently
attended to.

The commissioners appointed to examine into the methods
proposed for preventing the forgery of bank-notes, state in their
report, that out of one hundred and seventy-eight projects
communicated to the bank and to the commissioners, there were
only twelve of superior skill, and nine which it was necessary
more particularly to examine.

319. It is however a curious circumstance, that although the
power of combining machinery is so common, yet the more beautiful
combinations are exceedingly rare. Those which command our
admiration equally by the perfection of their effects and the
simplicity of their means, are found only amongst the happiest
productions of genius.

To produce movements even of a complicated kind is not
difficult. There exist a great multitude of known contrivances
for all the more usual purposes, and if the exertion of moderate
power is the end of the mechanism to be contrived, it is possible
to construct the whole machine upon paper, and to judge of the
proper strength to be given to each part as well as to the
framework which supports it, and also of its ultimate effect,
long before a single part of it has been executed. In fact, all
the contrivance, and all the improvements, ought first to be
represented in the drawings.

320. On the other hand, there are effects dependent upon
physical or chemical properties for the determination of which no
drawings will be of any use. These are the legitimate objects of
direct trial. For example; if the ultimate result of an engine is
to be that it shall impress letters on a copperplate by means of
steel punches forced into it, all the mechanism by which the
punches and the copper are to be moved at stated intervals, and
brought into contact, is within the province of drawing, and the
machinery may be arranged entirely upon paper. But a doubt may
reasonably spring up, whether the bur that will be raised round
the letter, which has been already punched upon the copper, may
not interfere with the proper action of the punch for the letter
which is to be punched next adjacent to it. It may also be feared
that the effect of punching the second letter, if it be
sufficiently near to the first, may distort the form of that
first figure. If neither of these evils should arise, still the
bur produced by the punching might be expected to interfere with
the goodness of the impression produced by the copperplate; and
the plate itself, after having all but its edge covered with
figures, might change its form, from the unequal condensation
which it must suffer in this process, so as to render it very
difficult to take impressions from it at all. It is impossible by
any drawings to solve difficulties such as these, experiment
alone can determine their effect. Such experiments having been
made, it is found that if the sides of the steel punch are nearly
at right angles to the face of the letter, the bur produced is
very inconsiderable; that at the depth which is sufficient for
copperplate printing, no distortion of the adjacent letters takes
place, although those letters are placed very close to each
other; that the small bur which arises may easily be scraped off;
and that the copperplate is not distorted by the condensation of
the metal in punching, but is perfectly fit to print from, after
it has undergone that process.

321. The next stage in the progress of an invention, after
the drawings are finished and the preliminary experiments have
been made, if any such should be requisite, is the execution of
the machine itself. It can never be too strongly impressed upon
the minds of those who are devising new machines, that to make
the most perfect drawings of every part tends essentially both to
the success of the trial, and to economy in arriving at the
result. The actual execution from working drawings is
comparatively an easy task; provided always that good tools are
employed, and that methods of working are adopted, in which the
perfection of the part constructed depends less on the personal
skill of the workman, than upon the certainty of the method
employed.

322. The causes of failure in this stage most frequently
derive their origin from errors in the preceding one; and it is
sufficient merely to indicate a few of their sources. They
frequently arise from having neglected to take into consideration
that metals are not perfectly rigid but elastic. A steel cylinder
of small diameter must not be regarded as an inflexible rod; but
in order to ensure its perfect action as an axis, it must be
supported at proper intervals.

Again, the strength and stiffness of the framing which
supports the mechanism must be carefully attended to. It should
always be recollected, that the addition of superfluous matter to
the immovable parts of a machine produces no additional momentum,
and therefore is not accompanied with the same evil that arises
when the moving parts are increased in weight. The stiffness of
the framing in a machine produces an important advantage. If the
bearings of the axis (those places at which they are supported)
are once placed in a straight line, they will remain so, if the
framing be immovable; whereas if the framework changes its form,
though ever so slightly, considerable friction is immediately
produced. This effect is so well understood in the districts
where spinning factories are numerous, that, in estimating the
expense of working a new factory, it is allowed that five per
cent on the power of the steam-engine will be saved if the
building is fireproof: for the greater strength and rigidity of a
fireproof building prevents the movement of the long shafts or
axes which drive the machinery, from being impeded by the
friction that would arise from the slightest deviation in any of
the bearings.

323. In conducting experiments upon machinery, it is quite a
mistake to suppose that any imperfect mechanical work is good
enough for such a purpose. If the experiment is worth making, it
ought to be tried with all the advantages of which the state of
mechanical art admits; for an imperfect trial may cause an idea
to be given up, which better workmanship might have proved to be
practicable. On the other hand, when once the efficiency of a
contrivance has been established, with good workmanship it will
be easy afterwards to ascertain the degree of perfection which
will suffice for its due action.

324. It is partly owing to the imperfection of the original
trials, and partly to the gradual improvements in the art of
making machinery, that many inventions which have been tried, and
given up in one state of art, have at another period been
eminently successful. The idea of printing by means of moveable
types had probably suggested itself to the imagination of many
persons conversant with impressions taken either from blocks or
seals. We find amongst the instruments discovered in the remains
of Pompeii and Herculaneum, stamps for words formed out of one
piece of metal, and including several letters. The idea of
separating these letters, and of recombining them into other
words, for the purpose of stamping a book, could scarcely have
failed to occur to many: but it would almost certainly have been
rejected by those best acquainted with the mechanical arts of
that time; for the workmen of those days must have instantly
perceived the impossibility of producing many thousand pieces of
wood or metal, fitting so perfectly and ranging so uniformly, as
the types or blocks of wood now used in the art of printing.

The principle of the press which bears the name of Bramah,
was known about a century and a half before the machine, to which
it gave rise, existed; but the imperfect state of mechanical art
in the time of the discoverer, would have effectually deterred
him, if the application of it had occurred to his mind, from
attempting to employ it in practice as an instrument for exerting
force.

These considerations prove the propriety of repeating, at the
termination of intervals during which the art of making machinery
has received any great improvement, the trails of methods which,
although founded upon just principles, had previously failed.

325. When the drawings of a machine have been properly made,
and the parts have been well executed, and even when the work it
produces possesses all the qualities which were anticipated,
still the invention may fail; that is, it may fail of being
brought into general practice. This will most frequently arise
from the circumstance of its producing its work at a greater
expense than that at which it can be made by other methods.

326. Whenever the new, or improved machine, is intended to
become the basis of a manufacture, it is essentially requisite
that the whole expense attending its operations should be fully
considered before its construction is undertaken. It is almost
always very difficult to make this estimate of the expense: the
more complicated the mechanism, the less easy is the task; and in
cases of great complexity and extent of machinery it is almost
impossible. It has been estimated roughly, that the first
individual of any newly invented machine, will cost about five
times as much as the construction of the second, an estimate
which is, perhaps, sufficiently near the truth. If the second
machine is to be precisely like the first, the same drawings, and
the same patterns will answer for it; but if, as usually happens,
some improvements have been suggested by the experience of the
first, these must be more or less altered. When, however, two or
three machines have been completed, and many more are wanted,
they can usually be produced at much less than one-fifth of the
expense of the original invention.

327. The arts of contriving, of drawing, and of executing, do
not usually reside in their greatest perfection in one
individual; and in this, as in other arts, the division of labour
must be applied. The best advice which can be offered to a
projector of any mechanical invention, is to employ a respectable
draughtsman; who, if he has had a large experience in his
profession, will assist in finding out whether the contrivance is
new, and can then make working drawings of it. The first step,
however, the ascertaining whether the contrivance has the merit
of novelty, is most important; for it is a maxim equally just in
all the arts, and in every science, that the man who aspires to
fortune or to fame by new discoveries, must be content to examine
with care the knowledge of his contemporaries, or to exhaust his
efforts in inventing again, what he will most probably find has
been better executed before.

328. This, nevertheless, is a subject upon which even
ingenious men are often singularly negligent. There is, perhaps,
no trade or profession existing in which there is so much
quackery, so much ignorance of the scientific principles, and of
the history of their own art, with respect to its resources and
extent, as are to be met with amongst mechanical projectors. The
self-constituted engineer, dazzled with the beauty of some,
perhaps, really original contrivance, assumes his new profession
with as little suspicion that previous instruction, that thought
and painful labour, are necessary to its successful exercise, as
does the statesman or the senator. Much of this false confidence
arises from the improper estimate which is entertained of the
difficulty of invention in mechanics. It is, therefore, of great
importance to the individuals and to the families of those who
are too often led away from more suitable pursuits, the dupes of
their own ingenuity and of the popular voice, to convince both
them and the public that the power of making new mechanical
combinations is a possession common to a multitude of minds, and
that the talents which it requires are by no means of the highest
order. It is still more important that they should be impressed
with the conviction that the great merit, and the great success
of those who have attained to eminence in such matters, was
almost entirely due to the unremitted perseverance with which
they concentrated upon their successful inventions the skill and
knowledge which years of study had matured.