On the Economy of Machinery and Manufactures - Charles Babbage (interesting books to read in english .TXT) 📗

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 twothirds 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 steamengine 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 banknotes, 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,