CHAPTER 7.

Exerting Forces Too Great for Human Power, and Executing
Operations Too Delicate for Human Touch

56. It requires some skill and a considerable apparatus to
enable many men to exert their whole force at a given point; and
when this number amounts to hundreds or to thousands, additional
difficulties present themselves. If ten thousand men were hired
to act simultaneously, it would be exceedingly difficult to
discover whether each exerted his whole force, and consequently,
to be assured that each man did the duty for which he was paid.
And if still larger bodies of men or animals were necessary, not
only would the difficulty of directing them become greater, but
the expense would increase from the necessity of transporting
food for their subsistence.

The difficulty of enabling a large number of men to exert
their force at the same instant of time has been almost obviated
by the use of sound. The whistle of the boatswain performs this
service on board ships; and in removing, by manual force, the
vast mass of granite, weighing above 1,400 tons, on which the
equestrian figure of Peter the Great is placed at St Petersburgh,
a drummer was always stationed on its summit to give the signal
for the united efforts of the workmen.

An ancient Egyptian drawing was discovered a few years since,
by Champollion, in which a multitude of men appeared harnessed to
a huge block of stone, on the top of which stood a single
individual with his hands raised above his head, apparently in
the act of clapping them, for the purpose of insuring the
exertion of their combined force at the same moment of time.

57. In mines, it is sometimes necessary to raise or lower
great weights by capstans requiring the force of more than one
hundred men. These work upon the surface; but the directions must
be communicated from below, perhaps from the depth of two hundred
fathoms. This communication, however, is accomplished with ease
and certainty by signals: the usual apparatus is a kind of
clapper placed on the surface close to the capstan, so that every
man may hear, and put in motion from below by a rope passing up
the shaft.

At Wheal Friendship mine in Cornwall, a different contrivance
is employed: there is in that mine an inclined plane, passing
underground about two-thirds of a mile in length. Signals are
communicated by a continuous rod of metal, which being struck
below, the blow is distinctly heard on the surface.

58. In all our larger manufactories numerous instances occur
of the application of the power of steam to overcome resistances
which it would require far greater expense to surmount by means
of animal labour. The twisting of the largest cables, the
rolling, hammering, and cutting large masses of iron, the
draining of our mines, all require enormous exertions of physical
force continued for considerable periods of time. Other means are
had recourse to when the force required is great, and the space
through which it is to act is small. The hydraulic press of
Bramah can, by the exertion of one man, produce a pressure of
1,500 atmospheres; and with such an instrument a hollow cylinder
of wrought iron three inches thick has been burst. In rivetting
together the iron plates, out of which steam-engine boilers are
made, it is necessary to produce as close a joint as possible.
This is accomplished by using the rivets red-hot: while they are
in that state the two plates of iron are rivetted together, and
the contraction which the rivet undergoes in cooling draws them
together with a force which is only limited by the tenacity of
the metal of which the rivet itself is made.

59. It is not alone in the greater operations of the engineer
or the manufacturer, that those vast powers which man has called
into action, in availing himself of the agency of steam, are
fully developed. Wherever the individual operation demanding
little force for its own performance is to be multiplied in
almost endless repetition, commensurate power is required. It is
the same 'giant arm' which twists 'the largest cable', that spins
from the cotton plant an 'almost gossamer thread'. Obedient to
the hand which called into action its resistless powers, it
contends with the ocean and the storm, and rides triumphant
through dangers and difficulties unattempted by the older modes
of navigation. It is the same engine that, in its more regulated
action, weaves the canvas it may one day supersede, or, with
almost fairy fingers, entwines the meshes of the most delicate
fabric that adorns the female form.(1*)

60. The Fifth Report of the Select Committee of the House of
Commons on the Holyhead Roads furnishes ample proof of the great
superiority of steam vessels. The following extracts are taken
from the evidence of Captain Rogers, the commander of one of the
packets:

Question. Are you not perfectly satisfied, from the experience
you have had, that the steam vessel you command is capable of
performing what no sailing vessel can do?
Answer. Yes.

Question. During your passage from Gravesend to the Downs, could
any square-rigged vessel, from a first-rate down to a sloop of
war, have performed the voyage you did in the time you did it in
the steamboat?
Answer. No: it was impossible. In the Downs we passed several
Indiamen, and 150 sail there that could not move down the
channel: and at the back of Dungeness we passed 120 more.

Question. At the time you performed that voyage, with the weather
you have described, from the Downs to Milford, if that weather
had continued twelve months, would any square-rigged vessel have
performed it?
Answer. They would have been a long time about it: probably,
would have been weeks instead of days. A sailing vessel would not
have beat up to Milford, as we did, in twelve months.


61. The process of printing on the silver paper, which is
necessary for bank-notes, is attended with some inconvenience,
from the necessity of damping the paper previously to taking the
impression. It was difficult to do this uniformly and in the old
process of dipping a parcel of several sheets together into a
vessel of water, the outside sheets becoming much more wet than
the others, were very apt to be torn. A method has been adopted
at the Bank of Ireland which obviates this inconvenience. The
whole quantity of paper to be damped is placed in a close vessel
from which the air is exhausted; water is then admitted, and
every leaf is completely wetted; the paper is then removed to a
press, and all the superfluous moisture is squeezed out.

62. The operation of pulverizing solid substances and of
separating the powders of various degrees of fineness, is common
in the arts: and as the best graduated sifting fails in effecting
this separation with sufficient delicacy, recourse is had to
suspension in a fluid medium. The substance when reduced by
grinding to the finest powder is agitated in water which is then
drawn off: the coarsest portion of the suspended matter first
subsides, and that which requires the longest time to fall down
is the finest. In this manner even emery powder, a substance of
great density, is separated into the various degrees of fineness
which are required. Flints, after being burned and ground, are
suspended in water, in order to mix them intimately with clay,
which is also suspended in the same fluid for the formation of
porcelain. The water is then in part evaporated by heat, and the
plastic compound, out of which our most beautiful porcelain is
formed, remains. It is a curious fact, and one which requires
further examination than it has yet received, that, if this
mixture be suffered to remain long at rest before it is worked
up, it becomes useless; for it is then found that the silex,
which at first was uniformly mixed, becomes aggregated together
in small lumps. This parallel to the formation of flints in the
chalk strata deserves attention.(2*)

63. The slowness with which powders subside, depends partly
on the specific gravity of the substance, and partly on the
magnitude of the particles themselves. Bodies, in falling through
a resisting medium, after a certain time acquire a uniform
velocity, which is called their terminal velocity, with which
they continue to descend: when the particles are very small, and
the medium dense, as water, this terminal velocity is soon
arrived at. Some of the finer powders even of emery require
several hours to subside through a few feet of water, and the mud
pumped up into our cisterns by some of the water companies is
suspended during a still longer time. These facts furnish us with
some idea of the great extent over which deposits of river mud
may be spread; for if the mud of any river whose waters enter the
Gulf Stream, sink through one foot in an hour, it might be
carried by that stream 1,500 miles before it had sunk to the
depth of 600 or 700 feet.

64. A number of small filaments of cotton project from even
the best spun thread, and when this thread is woven into muslin
they injure its appearance. To cut these off separately is quite
impossible, but they are easily removed by passing the muslin
rapidly over a cylinder of iron kept at a dull red heat: the time
during which each portion of the muslin is in contact with the
red-hot iron is too short to heat it to the burning point; but
the filaments being much finer, and being pressed close to the
hot metal, are burnt.

The removal of these filaments from patent net is still more
necessary for its perfection. The net is passed at a moderate
velocity through a flame of gas issuing from a very long and
narrow slit. Immediately above the flame a long funnel is fixed,
which is connected with a large air-pump worked by a
steam-engine. The flame is thus drawn forcibly through the net,
and all the filaments on both sides of it are burned off at one
operation. Previously to this application of the air-pump, the
net acting in the same way, although not to the same extent, as
the wire-gauze in Davy's safety lamp, cooled down the flame so as
to prevent the combustion of the filaments on the upper side: the
air-pump by quickening the current of ignited gas, removes this
inconvenience.

NOTES:

1. The importance and diversified applications of the steam
engine were most ably enforced in the speeches made at a public
meeting held (June 1824) for the purpose of proposing the
erection of a monument to the memory of James Watt; these were
subsequently printed.

2. Some observations on the subject, by Dr Fitton, occur in the
appendix to Captain King's Survey of the Coast of Australia, vol.
ii, p. 397. London, 1826.