The Cassava Press and its Structure.--Mode of using it.--The
Siamese Link.--An ingenious Robbery.--Muscles and their Mode of
Action.--Human Arms and Steelyard.--Change of Direction.--The Human
Hand and Wrist.--Story of a Carpenter.--The Pulley.--Reduction by
Friction.--Past and present Engines.--Oiling Machines.--Treatment
of the Sewing Machine.--Use of Paraffine.--Disuse of Machine
hurtful.--Human Joints.--Synovia and its Value.--Disuse of Joints
hurtful.--The Lazy-tongs and its Usefulness to
Invalids.--Suggestions for Improvement.--Larva of the Dragonfly and
its Mask.--Curious Mode of seizing Prey.--Proboscis of the
Housefly, and Mode of using it.--The Apple-parer.--Squirrel and
Nut.--Structure of Teeth.--Rock-splitting.--Powers of Ice.--How the
Pebble-ridge is formed.--Splitting Stones by Moisture.--The Diamond
Drill.--Ovipositor of the Gad-fly.--Curious Similitude of
Structure.
MEANS AND APPLIANCES.
In this chapter we will take some miscellaneous appliances of force both
in Art and Nature.
In the accompanying illustration is shown the Cassava Press of Southern
America, a most effective and simple instrument for extracting the
juices of the root. These juices are poisonous when raw, but, when
properly boiled and cooked, they make an excellent sauce.
The press in question is an elastic tube made of flat strips of cane
woven together exactly like the “Siamese Link,” which will be presently
described. The cassava root, after having been scraped until it
resembles horseradish, is forced into the press until it can hold no
more. The result is, that the tube is shortened and thickened, being
widest in the middle.
It is then hung by its upper loop to the horizontal beam of a hut. A
long pole is passed through the lower loop, the short end is placed
under a projecting peg on the upright post of the house, and a heavy
weight attached to the longer end. A powerful leverage is thus obtained,
the tube is forcibly shortened, and the juice exudes through the
apertures of the woven cane.
[Illustration: CASSAVA PRESS.]
When it begins to run slowly, a woman seats herself at the end of the
pole, so as to increase its weight. I must mention here that in the
illustration the press is too near the middle of the pole. This is
because the exigences of our page do not admit of the requisite length.
But if the reader will kindly assume the end to which the stone is
attached to be three or four times longer, he will have an idea of the
great power which is exerted upon the cassava.
On the left hand of the illustration is the same cassava press as seen
when empty, and both figures, as well as that of the pot for receiving
the juice, are taken from specimens in my collection.
* * * * *
ON the right hand of the following illustration is the Siamese Link,
which caused such a sensation when it first came out.
A finger is inserted at each end, and, when the owner attempts to
withdraw them, the Link contracts, and the harder the pull, the tighter
is the hold. If the fourth instead of the first finger be employed, the
hold of the Link is exceedingly strong.
The only mode of release is by pushing the fingers together, when the
Link will relax. It should then be held by the remaining fingers of one
hand, so that it shall not contract again, and the finger of the other
hand comes out at once.
An ingenious robbery was once committed by means of the Siamese Link. A
man of good address struck up an acquaintance with a jeweller. One day
he produced a Siamese Link, and challenged him to get his fingers out
when once they were in. So the jeweller was told to put his hands behind
his back, and push his little fingers as far in as he could.
[Illustration: MUSCLES Of LEG.]
[Illustration: SIAMESE LINK.]
This he did, when the treacherous friend made a clean sweep of all the
rings, brooches, ear-rings, and such jewellery as was within his reach,
while the unfortunate jeweller was vainly tugging at the Link. This only
occupied a few seconds for a practised hand, and the thief quietly
opened the door, shut it, and was lost in the passing crowd before the
jeweller could recover from his surprise.
* * * * *
ON the left of the same illustration is a view of the muscles of the
human leg, which, as the reader will see, are curiously like the
distended cassava press. Although the mode of applying the force
differs, the principle is the same.
In the latter case an external force is applied to the press, but in the
latter an internal, or rather a central, force is applied to the bones.
It is evident that if a similar process were carried on with the cassava
press, and the central portion forcibly distended, the supports at
either end would be drawn powerfully towards each other. Substitute the
muscle for the press, and the bones for the poles, and this is muscular
action.
* * * * *
HERE we have a diagram which speaks for itself, as far as muscular
action is concerned, but there is another point to which we shall
presently pass.
[Illustration: HUMAN ARM.]
[Illustration: STEELYARD.]
The muscle of the arm is seen running along the bone, passing over the
elbow, where it is held down by a tendinous band, and, by its
contraction, enabling the arm to be bent so as to uphold a considerable
weight. The mechanical analogy between this arrangement and the common
Steelyard is too evident to need any explanation except inspection of
the diagram.
* * * * *
THERE is, however, another point which is worthy of consideration. The
muscle does not proceed at once from the shoulder to the wrist, but
passes under the tendinous band above mentioned, and so produces a
change of direction when the arm is bent.
There is a more complicated arrangement of a similar character in the
human hand, a diagram of which is given in the left-hand figure of the
accompanying illustration.
The fingers are, of course, moved by a set of tendons, and the muscles,
from which these tendons spring, are attached to the fore-arm (I
purposely omit the scientific titles, though they would be much easier
to write). Any of my readers can prove this for themselves.
Let him first grasp the upper arm firmly, and bend the limbs, and he
will at once find that the swelling of the muscle shows the source of
power.
Then let him do the same, but grasp the fore-arm, and he will find that
the muscles are quiescent, showing that the former set of muscles belong
to the entire arm, and not to the fingers, while the muscles of the
lower arm have nothing to do with the bending of that limb.
Now let him grasp the fore-arm, and open and close the fingers, and he
will feel a whole set of muscles rise, and swell and harden under his
grasp. Next let him bend his hand inwards, and he will find that the
fingers work perfectly well, though the direction of force is changed.
This is owing to a band of tendons passing across the wrist, under which
the finger-tendons play. The course of the tendons is marked in the
illustration by leaving them white.
The wondrous structure of the human hand and its multitudinous tendons
can only be appreciated by actual dissection, but an idea of their
variety and use may be obtained by watching the hands of a skilful
pianoforte-player. This struck me forcibly the first time that I ever
heard Thalberg play.
While on the subject of tendons, I may mention a curious case. A
journeyman carpenter missed a blow with his axe, and struck his left
hand at the junction of the thumb and wrist. The important tendon was
severed, and the inner muscles, having no counteracting force, dragged
the thumb into the hollow of the hand.
To all appearance, the man could no longer earn a living as a carpenter.
But he would not be discouraged, and while he was in hospital he
borrowed a book, and studied the anatomy of the human hand. By means of
this knowledge he constructed a sort of semi-glove, in which he
introduced pieces of watch-spring, that supplied the place of the lost
tendon.
Not content with this, he studied Euclid for the purposes of his trade,
so as to get the most possible out of a piece of wood of given
dimensions, and be able to go straight to his mark by a problem, instead
of doing it slowly and clumsily with a two-foot rule and a pair of
compasses. When I saw him last he was a master carpenter in a large and
increasing business.
Man has unconsciously imitated Nature in the invention of the Pulley,
whereby the direction of force may be altered almost at will. In this
case the cord takes the part of the working tendon, and the Pulley of
the fixed tendinous crossbar. There is much matter of interest in the
tendons, but, as our space is fast waning, I must resist the temptation
of describing them.
* * * * *
IN all machinery one of the chief objects of the machinist is to reduce
friction as much as possible. He makes all the joints as smooth as tools
can polish, and always introduces oil or some lubricating substance into
the joints. Otherwise the engine rattles with a noise proportionate to
its power, and wastes its force on the friction.
[Illustration: TENDONS OF HAND.]
[Illustration: PULLEY.]
In my childish days a steam-engine of any kind used to rattle so loudly
that conversation was almost impossible. Now they are made with such
perfection, that the vast engines in use at the pumping stations of the
metropolitan drainage are almost absolutely silent.
There is the enormous hall, filled with gigantic beams and rods, and
cranks, and wheels. A single man turns a little handle, and the whole
machinery starts into life. Beams rock, cranks and wheels revolve, rods
slide up and down, and all in a silence which is nearly appalling in its
manifestation of unassuming strength. Indeed, many a hand sewing
machine makes far more noise than one of those giant engines, and all
because in the latter friction is avoided as far as possible, every
screw is well braced up, and every joint is kept well lubricated.
Here I may observe that few sewing machines get fair play. They rattle,
they squeak, they become stiffer daily, they snap the thread, and then
decline work altogether. And in almost every case this is done by
neglect on the part of the owner, who does not lubricate every point of
the machine which works upon another.
[Illustration: LUBRICATION OF JOINT.]
[Illustration: OILING MACHINE.]
Ladies especially are very careless in this respect, and will mostly
omit three or four of the oiling points. They might just as well omit
them all, as a single unoiled point will disarrange the harmonious
motion of the whole machine. I have often been called in as surgeon in
such cases, and have almost invariably been able to point to several
spots which needed oil, and did not get it. Sometimes, out of false
economy, an inferior oil is used, which speedily clogs and hardens, and
stops all movement. In such a case the best remedy is to apply paraffine
liberally, and use it for a quarter of an hour or so. It will soon
dissolve the clogged oil, which may be worked out by turning the handle
or crank of the machine.
Of course the best remedy is to take the machine to pieces, polish the
joints, lubricate them, and put it together again. But this is a
perilous process, and an amateur, if he tries it, will generally find
himself with half-a-dozen pieces for which he can find no place.
Paraffine will answer every purpose, and I have released many a
stiffened machine by its use.
Then some people leave their machines untouched for days, or even weeks,
and then wonder that they work stiffly. Every day the machine should he
worked, if only for a few seconds, and then it will seldom stiffen. It
is just the same with steamers. When they are in harbour, though the
fires be out, and they are not meant to move for weeks, the engines are
always turned round at least once daily.
* * * * *
BOTH these rules hold good in the animal kingdom.
To every joint there are attached certain glands that supply a kind of
oily substance technically named “synovia,” which acts exactly the same
part as the oil or grease of machinery. If these glands do not do their
duty, and the supply of synovia be defective, the joints become stiff,
painful, and crackle when they are moved.
Then, exactly as the joints of a machine become stiff from non-usage, so
do those of a human being. We will take, for example, the Indian Fakirs
who vow that they will not move some limb from a definite posture. At
first the exertion is trying and painful, but by degrees the disused
joints lose their faculty of motion, and, even if their owner wished to
move a limb, he could not do it.
The right-hand figure of the illustration represents the lubrication of
an ordinary sewing machine, and the left-hand figure is a section of the
human knee-joint, showing the gland which supplies the synovia.
* * * * *
PERHAPS some of my readers may think that such a subject as the
“Lazy-tongs” is too trivial for a work which deals, however lightly,
with science. But there may be some who know the inestimable benefit of
Lazy-tongs under certain conditions.
There are many cases where a severe injury has occurred, or where
rheumatism has fixed its tiger-claws in the joints, so that movement is
all but impossible. There may be no one in the room to help the invalid,
and even to stretch the arm over the table is as impossible as to jump
over the house.
Then it is that the real value of the Lazy-tongs becomes manifested, and
that it shows itself in the light of a supplementary limb. With a mere
movement of the fingers it can be stretched across any table which is
likely to be placed before an invalid, and seize the required object by
the tongs at the further end.
The only drawback to its use is, that the instrument cannot be shortened
without opening the tongs. But, if some plan could be devised whereby
the tongs could retain their hold under those conditions, the instrument
would be a perfect one.
* * * * *
EXACTLY such a Lazy-tongs we have in Nature, in the well-known “mask of
the larva and pupa of the Dragon-fly.” It is called a mask because, when
closed, it covers the face.
[Illustration: HEAD AND PROBOSCIS OF HOUSE-FLY.]
[Illustration: MASK OF DRAGON-FLY LARVA.]
[Illustration: LAZY-TONGS.]
It chiefly consists of two flat, horny plates, hinged in each other like
a carpenter’s two-foot rule, and being capable of extension to a
considerable length. The end is widened, and furnished with two jaws,
which take the part of the tongs in the instrument above described.
This curious apparatus is used for the purpose of securing prey.
I have kept many of these creatures, and watched their mode of feeding.
As has already been mentioned, they have two modes of progression,
_i.e._ walking by means of legs like those of ordinary insects; and
driving themselves along by ejecting water from the tail, on the
principle of the rocket. As far as I have seen, the latter mode is
always used in taking prey. The Dragon-fly larva always lives at the
bottom of the water, though it can force itself to the surface if
needful. And, like the dreaded ground-shark, it seizes its prey from
beneath.
Its favourite food is the larva of the whirlwig-beetle, a fat white
grub, with a number of white, soft, feathery gills fringing its sides.
In order to produce a current of air over these gills, the larva
wriggles itself up to a height of several inches, and then sinks slowly
down, with the white gills floating on either side.
Should a Dragon-fly larva be near, it sees the grub ascending, glides
quietly under it without using its legs so as to cause alarm, waits for
it to sink, darts out the mask, seizes it in the jaws, drags it to its
mouth, and the grub is seen no more. So voracious are these larvæ, that,
if only two are kept in the same vessel, one is sure to devour the
other.
* * * * *
ANOTHER good example of the Lazy-tongs is the Proboscis of the common
House-fly. We have all seen these insects alight near sugar, or any
other tempting food, unfold the proboscis, pour a drop of liquid in the
sugar, dissolve it, suck it up, and then shut up the proboscis as if by
hinges.
* * * * *
ANOTHER labour-saving machine is the Apple-parer, a comparatively modern
invention. The principle is, that a knife is pressed lightly by a spring
against a revolving apple, and set at such an angle that nothing but the
outside peel can be removed. Where large numbers of apples have to be
pared, as in making preserves or in hotels, this is a most useful
invention.
[Illustration: SQUIRREL AND NUT.]
[Illustration: APPLE PARER.]
When I first saw it at work, the operation seemed familiar to me, but I
could not at first remember the parallel. At last it flashed across me
that a Squirrel eating a nut was the natural parallel of the Paring
Machine.
After splitting the shell and extracting the kernel, the Squirrel takes
the latter between its fore-paws, presses it against its upper incisor
teeth, and makes it revolve rapidly. In a second or two the kernel is
perfectly peeled, and is then eaten.
In this case the incisor teeth of the Squirrel take the part of the
knife, the muscles of the leg that of the spring, and the sharp edges of
the upper teeth that of the knife. The structure of the Rodent teeth has
already been explained in page 233.
* * * * *
THE wonderful effects of water in breaking up the hardest rock have
already been described. We will now proceed to another branch of the
same subject.
[Illustration: FROST-CLEFT ROCK.]
[Illustration: STONE-SPLITTING.]
Perhaps some of my readers may have wandered along our rocky coasts, and
have seen how large masses of rock are continually detaching themselves,
though they are so hard that a cold chisel is needed to make any
impression upon them.
Then they fall into the sea, and are rolled backwards and forwards until
they become smoothed and rounded, and are called pebbles, while the
portion that is rubbed off them is called sand. The phenomenon is well
shown in the wonderful Pebble Ridge of North Devon.
The real agent is ice.
We all know that, when water freezes, it expands considerably. This
accounts for two phenomena.
First, as it expands, it becomes lighter than water, and consequently
floats on the surface.
Next, there are few of us who have not seen water-bottles cracked by
the freezing of the water. The most common, and perhaps the most
unpleasant, example of this propensity is the bursting of water-pipes in
the winter, followed by a flooding of the house when the thaw comes.
This is caused by the expansion of the frozen water, which will burst
not only a thin leaden tube, but a stout iron vessel. Care should
therefore be taken, at the beginning of winter, to cover up all exposed
portions of leaden pipes, and there will then be no danger. There was
one pipe in my house that was always bursting, but after I covered it
with two or three layers of carpet placed loosely over each other, so as
to entangle the air and form a non-conductor, the pipe has never frozen,
and the water supply has been uninterrupted by the severest frosts.
I am told that a still better plan exists, especially in places where
the pipes cannot be thoroughly protected by external wrappings. Let six
inches or so of the leaden pipe be removed, and its place supplied by a
vulcanised india-rubber tube.
The ice _must_ expand somewhere, and chooses the spot where least
resistance is offered to it. Consequently, it expands in the
india-rubber tube, but does not break it, and, when the thaw comes,
there is no overflow of water.
* * * * *
MAN utilises this power of ice in stone-splitting. Instead of taking the
trouble to cut the stone by manual labour, the workmen bore a series of
holes, fill them with water, insert tightly a wooden plug to prevent the
ice, when formed, from oozing out of the holes, and leave the rest for
the frost to do.
A like effect is produced in the warm weather by substituting similar
plugs, but quite dry, having been baked for hours in an oven, for the
purpose of driving out every particle of moisture. These plugs are
hammered into the holes as deeply as they will go, and there left. Even
if there be no rain, the nightly dews make their way into the pores of
the dry wood, and cause it to swell with such irresistible force that
the stone is split with scarcely any manual labour on the part of the
workmen.
* * * * *
YET another plan for cutting hard stones. Some of my readers may be
aware that a singularly ingenious instrument has been invented for
cutting boles in granite and other hard rocks. It is called the Diamond
Drill, because its tip is armed with uncut diamonds.
It is necessary that the diamond should not be cut, as the natural edges
are needed. A glazier’s diamond, for example, is always set as it came
out of the mine. The stories that are told about cutting out panes of
glass with a diamond ring are all absurd. A diamond, when it has once
passed through the hands of the jeweller, cannot cut glass. It can
scratch glass, but not one whit better than a flake of ordinary flint.
[Illustration: BORER OF ŒSTRUS.]
[Illustration: DIAMOND-HEADED BORER.]
It is found that the Diamond Drill works with wondrous rapidity, cutting
away the stone with ease, and suffering scarcely any damage itself. The
tube to the end of which the diamonds are fixed is generally made in
telescopic fashion, so as to allow it to penetrate deeply into the rock,
without the necessity of shifting the machine by which it is turned. I
need hardly say that its rate of speed is very great indeed.
* * * * *
OUR old friend, the Gad-fly, again affords an example of a parallel.
The ovipositor is tubular, telescopic, and furnished at the top with
five little hard, sharp, scaly knobs, which act the same part as the
diamonds of the mining tool. Even the scoop-like shape of the tip, and
the telescopic shaft, are almost identical in both instances.
USEFUL ARTS.