On the Economy of Machinery and Manufactures by Charles Babbage (novels to read in english .TXT) 📖
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turned more quickly on its axis, and when very soft and almost
incandescent, it is removed from the fire, and the velocity of
rotation being still continually increased, the opening enlarges
from the effect of the centrifugal force, at first gradually,
until at last the mouth suddenly expands or “flashes” out into one
large circular sheet of red hot glass. The neck of the original
globe, which is to become the outer part of the sheet, is left
thick to admit of this expansion, and forms the edge of the
circular plate of glass, which is called a “Table”. The centre
presents the appearance of a thick boss or prominence, called the
“Bull’s-eye”, at the part by which it was attached to the iron
rod.
43. The most frequent reason for employing contrivances for
diminishing velocity, arises from the necessity of overcoming
great resistances with small power. Systems of pulleys, the
crane, and many other illustrations, might also be adduced here
as examples; but they belong more appropriately to some of the
other causes which we have assigned for the advantages of
machinery. The common smoke-jack is an instrument in which the
velocity communicated is too great for the purpose required, and
it is transmitted through wheels which reduce it to a more
moderate rate.
44. Telegraphs are machines for conveying information over
extensive lines with great rapidity. They have generally been
established for the purposes of transmitting information during
war, but the increasing wants of man will probably soon render
them subservient to more peaceful objects.
A few years since the telegraph conveyed to Paris information
of the discovery of a comet, by M. Gambart, at Marseilles: the
message arrived during a sitting of the French Board of
Longitude, and was sent in a note from the Minister of the
Interior to Laplace, the President, who received it whilst the
writer of these lines was sitting by his side. The object in this
instance was, to give the earliest publicity to the fact, and to
assure to M. Gambart the title of its first discoverer.
At Liverpool a system of signals is established for the
purposes of commerce, so that each merchant can communicate with
his own vessel long before she arrives in the port.
NOTES:
1. See Transactions of the Society of Arts, 1826.
Extending the Time of Action of Forces
45. This is one of the most common and most useful of the
employments of machinery. The half minute which we daily devote
to the winding-up of our watches is an exertion of labour almost
insensible; yet, by the aid of a few wheels, its effect is spread
over the whole twenty-four hours. In our clocks, this extension
of the time of action of the original force impressed is carried
still further; the better kind usually require winding up once in
eight days, and some are occasionally made to continue in action
during a month, or even a year. Another familiar illustration may
be noticed in our domestic furniture: the common jack by which
our meat is roasted, is a contrivance to enable the cook in a few
minutes to exert a force which the machine retails out during the
succeeding hour in turning the loaded spit; thus enabling her to
bestow her undivided attention on the other important duties of
her vocation. A great number of automatons and mechanical toys
moved by springs, may be classed under this division.
46. A small moving power, in the shape of a jack or a spring
with a train of wheels, is often of great convenience to the
experimental philosopher, and has been used with advantage in
magnetic and electric experiments where the rotation of a disk of
metal or other body is necessary, thus allowing to the enquirer
the unimpeded use of both his hands. A vane connected by a train
of wheels, and set in motion by a heavy weight, has also, on some
occasions, been employed in chemical processes, to keep a
solution in a state of agitation. Another object to which a
similar apparatus may be applied, is the polishing of small
specimens of minerals for optical experiments.
Saving time in Natural Operations
47. The process of tanning will furnish us with a striking
illustration of the power of machinery in accelerating certain
processes in which natural operations have a principal effect.
The object of this art is to combine a certain principle called
tanning with every particle of the skin to be tanned. This, in
the ordinary process, is accomplished by allowing the skins to
soak in pits containing a solution of tanning matter: they remain
in the pits six, twelve, or eighteen months; and in some
instances (if the hides are very thick), they are exposed to the
operation for two years, or even during a longer period. This
length of time is apparently required in order to allow the
tanning matter to penetrate into the interior of a thick hide.
The improved process consists in placing the hides with the
solution of tan in close vessels, and then exhausting the air.
The effect is to withdraw any air which may be contained in the
pores of the hides, and to aid capillary attraction by the
pressure of the atmosphere in forcing the tan into the interior
of the skins. The effect of the additional force thus brought
into action can be equal only to one atmosphere, but a further
improvement has been made: the vessel containing the hides is,
after exhaustion, filled up with a solution of tan; a small
additional quantity is then injected with a forcing-pump. By
these means any degree of pressure may be given which the
containing vessel is capable of supporting; and it has been found
that, by employing such a method, the thickest hides may be
tanned in six weeks or two months.
48. The same process of injection might be applied to
impregnate timber with tar, or any other substance capable of
preserving it from decay, and if it were not too expensive, the
deal floors of houses might thus be impregnated with alumine or
other substances, which would render them much less liable to be
accidentally set on fire. In some cases it might be useful to
impregnate woods with resins, varnish, or oil; and wood saturated
with oil might, in some instances, be usefully employed in
machinery for giving a constant, but very minute supply of that
fluid to iron or steel, against which it is worked. Some idea of
the quantity of matter which can be injected into wood by great
pressure, may be formed, from considering the fact stated by Mr
Scoresby, respecting an accident which occurred to a boat of one
of our whaling-ships. The harpoon having been struck into the
fish, the whale in this instance, dived directly down, and
carried the boat along with him. On returning to the surface the
animal was killed, but the boat, instead of rising, was found
suspended beneath the whale by the rope of the harpoon; and on
drawing it up, every part of the wood was found to be so
completely saturated with water as to sink immediately to the
bottom.
49. The operation of bleaching linen in the open air is one
for which considerable time is necessary; and although it does
not require much labour, yet, from the risk of damage and of
robbery from long /exposure, a mode of shortening the process was
highly desirable. The method now practised, although not
mechanical, is such a remarkable instance of the application of
science to the practical purposes of manufactures, that in
mentioning the advantages derived from shortening natural
operations, it would have been scarcely pardonable to have
omitted all allusion to the beautiful application of chlorine, in
combination with lime, to the art of bleaching.
50. Another instance more strictly mechanical occurs in some
countries where fuel is expensive, and the heat of the sun is not
sufficient to evaporate the water from brine springs. The water
is first pumped up to a reservoir, and then allowed to fall in
small streams through faggots. Thus it becomes divided; and,
presenting a large surface, evaporation is facilitated, and the.
brine which is collected in the vessels below the faggots is
stronger than that which was pumped up. After thus getting rid of
a large part of the water, the remaining portion is driven off by
boiling. The success of this process depends on the condition of
the atmosphere with respect to moisture. If the air, at the time
the brine falls through the faggots, holds in solution as much
moisture as it can contain in an invisible state, no more can be
absorbed from the salt water, and the labour expended in pumping
is entirely wasted. The state of the air, as to dryness, is
therefore an important consideration in fixing the time when this
operation is to be performed; and an attentive examination of its
state, by means of the hygrometer, might be productive of some
economy of labour.
51. In some countries, where wood is scarce, the evaporation
of salt water is carried on by a large collection of ropes which
are stretched perpendicularly. In passing down the ropes, the
water deposits the sulphate of lime which it held in solution,
and gradually incrusts them, so that in the course of twenty
years, when they are nearly rotten, they are still sustained by
the surrounding incrustation, thus presenting the appearance of a
vast collection of small columns.
52. Amongst natural operations perpetually altering the
surface of our globe, there are some which it would be
advantageous to accelerate. The wearing down of the rocks which
impede the rapids of navigable rivers, is one of this class. A
very beautiful process for accomplishing this object has been
employed in America. A boat is placed at the bottom of the rapid,
and kept in its position by a long rope which is firmly fixed on
the bank of the river near the top. An axis, having a wheel
similar to the paddle-wheel of a steamboat fixed at each end of
it, is placed across the boat; so that the two wheels and their
connecting axis shall revolve rapidly, being driven by the force
of the passing current. Let us now imagine several beams of wood
shod with pointed iron fixed at the ends of strong levers,
projecting beyond the bow of the boat, as in the annexed
representation.
If these levers are at liberty to move up and down, and if
one or more projecting pieces, called cams, are fixed on the axis
opposite to the end of each lever, the action of the stream upon
the wheels will keep up a perpetual succession of blows. The
sharp-pointed shoe striking upon the rock at the bottom, will
continually detach small pieces, which the stream will
immediately carry off. Thus, by the mere action of the river
itself, a constant and most effectual system of pounding the rock
at its bottom is established. A single workman may, by the aid of
a rudder, direct the boat to any required part of the stream; and
when it is necessary to move up the rapid, as the channel is cut,
he can easily cause the boat to advance by means of a capstan.
53. When the object of the machinery just described has been
accomplished, and the channel is sufficiently deep, a slight
alteration converts the apparatus to another purpose almost
equally advantageous. The stampers and the projecting pieces on
the axis are removed, and a barrel of wood or metal, surrounding
part of the axis, and capable, at pleasure, of being connected
with, or disconnected from the axis itself, is substituted. The
rope which hitherto fastened
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