Transcriber's Note:
In text, italic is denoted by _underscores_ around the word/phrase.
The italic markup for single italicised letters (such as pounds and
pence symbols and in numbered lists) are deleted for easier reading.
Small capitals in the printed works have been transcribed as ALL
CAPITALS.
In chemical equations, underscores before bracketed numbers denote
a subscript, e.g. CO_{2} (carbon dioxide).
More Transcriber's Notes may be found at the end of this text.
THE ROMANCE OF
MODERN MECHANISM
[Illustration: A MECHANICAL SCULPTOR
The lower illustration shows the Wenzel Sculpturing Machine at work on
two blocks of stone ranged one on each side of a model. This machine
can make four copies simultaneously from one original. The upper
illustration shows the quality of work done by the automatic sculptor.]
THE ROMANCE OF
MODERN MECHANISM
WITH INTERESTING DESCRIPTIONS IN NON-TECHNICAL LANGUAGE OF WONDERFUL
MACHINERY AND MECHANICAL DEVICES AND MARVELLOUSLY DELICATE SCIENTIFIC
INSTRUMENTS, &c., &c.
BY
ARCHIBALD WILLIAMS,
B.A., OXON., F.R.G.S.
AUTHOR OF
"THE ROMANCE OF MODERN INVENTION," "THE ROMANCE OF MODERN MINING,"
"THE ROMANCE OF MODERN ENGINEERING," "THE ROMANCE OF MODERN
EXPLORATION," &c. &c.
WITH THIRTY ILLUSTRATIONS
LONDON
SEELEY AND CO. LIMITED
38 GREAT RUSSELL STREET
1910
_UNIFORM WITH THIS VOLUME_
THE LIBRARY OF ROMANCE
_Extra Crown 8vo. With many illustrations. 5s. each_
"Splendid volumes."--_The Outlook._
"This series has now won a considerable and well deserved
reputation."--_The Guardian._
"Each volume treats its allotted theme with accuracy, but at the same
time with a charm that will commend itself to readers of all ages.
The root idea is excellent, and it is excellently carried out, with
full illustrations and very prettily designed covers."--_The Daily
Telegraph._
By Prof. G. F. SCOTT ELLIOT, M.A., B.Sc.
THE ROMANCE OF SAVAGE LIFE
THE ROMANCE OF PLANT LIFE
THE ROMANCE OF EARLY BRITISH LIFE
By EDWARD GILLIAT, M.A.
THE ROMANCE OF MODERN SIEGES
By JOHN LEA, M.A.
THE ROMANCE OF BIRD LIFE
By JOHN LEA, M.A., & H. COUPIN, D.Sc.
THE ROMANCE OF ANIMAL ARTS AND CRAFTS
By SIDNEY WRIGHT
THE ROMANCE OF THE WORLD'S FISHERIES
By the Rev. J. C. LAMBERT, M.A., D.D.
THE ROMANCE OF MISSIONARY HEROISM
By G. FIRTH SCOTT
THE ROMANCE OF POLAR EXPLORATION
By ARCHIBALD WILLIAMS, B.A. (Oxon.), F.R.G.S.
THE ROMANCE OF EARLY EXPLORATION
THE ROMANCE OF MODERN EXPLORATION
THE ROMANCE OF MODERN MECHANISM
THE ROMANCE OF MODERN INVENTION
THE ROMANCE OF MODERN ENGINEERING
THE ROMANCE OF MODERN LOCOMOTION
THE ROMANCE OF MODERN MINING
By CHARLES R. GIBSON, A.I.E.E.
THE ROMANCE OF MODERN PHOTOGRAPHY
THE ROMANCE OF MODERN ELECTRICITY
THE ROMANCE OF MODERN MANUFACTURE
By EDMUND SELOUS
THE ROMANCE OF THE ANIMAL WORLD
THE ROMANCE OF INSECT LIFE
By AGNES GIBERNE
THE ROMANCE OF THE MIGHTY DEEP
By E. S. GREW, M.A.
THE ROMANCE OF MODERN GEOLOGY
By J. C. PHILIP, D.Sc., Ph.D.
THE ROMANCE OF MODERN CHEMISTRY
SEELEY & CO., LIMITED
INTRODUCTION
In the beginning a man depended for his subsistence entirely upon his
own efforts, or upon those of his immediate relations and friends. Life
was very simple in those days: luxury being unknown, and necessity the
factor which guided man's actions at every turn. With infinite labour
he ground a flint till it assumed the shape of a rough arrow-head, to
be attached to a reed and shot into the heart of some wild beast as
soon as he had approached close enough to be certain of his quarry.
The meat thus obtained he seasoned with such roots and herbs as nature
provided--a poor and scanty choice. Presently he discovered that
certain grains supported life much better than roots, and he became an
agriculturist. But the grain must be ground; so he invented a simple
mill--a small stone worked by hand over a large one; and when this
method proved too tedious he so shaped the stones' surfaces that they
touched at all points, and added handles by which the upper stone could
be revolved.
With the discovery of bronze, and, many centuries later, of iron, his
workshop equipment rapidly improved. He became an expert boat- and
house-builder, and multiplied weapons of offence and defence. Gradually
separate crafts arose. One man no longer depended on his individual
efforts, but was content to barter his own work for the products of
another man's labour, because it became evident that specialisation
promoted excellence of manufacture.
A second great step in advance was the employment of machinery, which,
when once fashioned by hand, saved an enormous amount of time and
trouble--the pump, the blowing bellows, the spinning-wheel, the loom.
But all had to be operated by human effort, sometimes replaced by
animal power.
With the advent of the steam-engine all industry bounded forward again.
First harnessed by Watt, Giant Steam has become a commercial and
political power. Everywhere, in mill and factory, locomotive, ship,
it has increased the products which lend ease and comfort to modern
life; it is the great ally of invention, and the ultimate agent for
transporting men and material from one point on the earth's surface to
another.
Try as we may, we cannot escape from our environment of mechanism,
unless we are content to revert to the loincloth and spear of the
savage. Society has become so complicated that the utmost efforts of
an individual are, after all, confined to a very narrow groove. The
days of the Jack-of-all-trades are over. Success in life, even bare
subsistence, depends on the concentration of one's faculties upon a
very limited daily routine. "Let the cobbler stick to his last" is a
maxim which carries an ever-increasing force.
The better to realise how dependent we are on the mechanisms controlled
by the thousand and one classes of workmen, let us consider the
surroundings, possessions, and movements of the average, well-to-do
business man.
At seven o'clock he wakes, and instinctively feels beneath his pillow
for his watch, a most marvellous assemblage of delicate parts shaped
by wonderful machinery. Before stepping into his bath he must turn a
tap, itself a triumph of mechanical skill. The razor he shaves with,
the mirror which helps him in the operation, the very brush and soap,
all are machine-made. With his clothes he adds to the burden of his
indebtedness to mechanism. The power-loom span the linen for his
shirts, the cloth for his outer garments. Shirts and collars are glossy
from the treatment of the steam laundry, where machinery is rampant.
His boots, kept shapely by machine-made lasts, should remind him that
mechanical devices have played a large part in their manufacture, very
possibly the human hand has scarcely had a single duty to perform.
He goes downstairs, and presses an electric button. Mechanism again.
While waiting for his breakfast his eye roves carelessly over the
knives, spoons, forks, table, tablecloth, wall-paper, engravings,
carpet, cruet-stand--all machine-made in a larger or less degree. The
very coals blazing in the grate were won by machinery; the marble
of the mantelpiece was shaped and polished by machinery; also the
fire-irons, the chairs, the hissing kettle. Machinery stares at him
from the loaf on its machine-made board. Machines prepared the land,
sowed, harvested, threshed, ground, and probably otherwise prepared
the grain for baking. Machines ground his salt, his coffee. Machinery
aided the capture of the tempting sole; helped to cure the rasher of
bacon; shaped the dishes, the plates, the coffee-pot.
Whirr-r-r! The motor-car is at the door, throbbing with the impulses of
its concealed machinery. Our friend therefore puts on his machine-made
gloves and hat and sallies forth. That wonderful motor, the product of
the most up-to-date, scientific, and mechanical appliances, bears him
swiftly over roads paved with machine-crushed stone and flattened out
by a steam-roller. A book might be reserved to the motor alone; but
we must refrain, for a few minutes' travel has brought the horseless
carriage to the railway station. Mr. Smith, being the holder of a
season ticket, does not trouble the clerk who is stamping pasteboards
with a most ingenious contrivance for automatically impressing dates
and numbers on them. He strolls out on the platform and buys the
morning paper, which, a few hours before, was being battered about
by one of the most wonderful machines that ever was devised by the
brain of man. Mr. Smith doesn't bother his head with thoughts of the
printing-press. Its products are all round him, in timetables and
advertisements. Nor does he ponder upon the giant machinery which
crushed steel ingots into the gleaming rails that stretch into the
far distance; nor upon the marvellous interlocking mechanism of the
signal-box at the platform-end; nor upon the electric wires thrumming
overhead. No! he had seen all these things a thousand times before, and
probably feels little of the romance which lies so thickly upon them.
A whistle blows. The "local" is approaching, with its majestic
locomotive--a very orgy of mechanism--its automatic brakes, its
thousand parts all shaped by mechanical devices,--steam saws, planes,
lathes, drills, hammers, presses. In obedience to a little lever the
huge mass comes quickly to rest; the steam pump on the engine commences
to gasp; a minute later another lever moves, and Mr. Smith is fairly on
his way to business.
Arrived at the metropolis, he presses electricity into his service,
either on an electric tram or on a subterranean train. In the latter
case he uses an electric lift, which lowers him into the bowels of the
earth, to pass him on to the current-propelled cars, driven by power
generated in far-away stations.
His office is stamped all over with the seal of mechanism. In the
lobby are girls hammering on marvellous typewriters; on his desk rests
a telephone, connected through wires and most elaborately equipped
exchanges with all parts of the country. To get at his private and
valuable papers Mr. Smith must have recourse to his bunch of keys,
which, with their corresponding locks, represent ingenuity of a high
degree. All day long he is in the grasp of mechanism; not even at lunch
time can he escape it, for the food set before him at the restaurant
has been cooked by the aid of special kitchen machinery.
And when the evening draws on Mr. Smith touches a switch to turn his
darkness into light, wrung through many wonderful processes from the
stored illumination of coal.
Were we to trace the daily round of the clerk, artisan, scientist,
engineer, or manufacturer, we should be brought into contact with a
thousand other mechanical appliances. Space forbids such a tour of
inspection; but in the following pages we may rove here and there
through the workshops of the world, gleaning what seems to be of
special interest to the general public, and weaving round it, with a
machine-made pen, some of the romance which is apt to be lost sight of
by the most marvellous of all creations--Man.
AUTHOR'S NOTE
THE author desires to express his indebtedness to the following
gentlemen for the kind help they have afforded him in connection with
the gathering of materials for the letterpress and illustration of this
book:--
The proprietors of _Cassier's Magazine_, _The Magazine of Commence_,
_The World's Work_, _The Motor Boat_; The Rexer Automatic Machine Gun
Co.; The Diesel Oil Engine Co.; The Cambridge Scientific Instrument
Co.; The Marconi Wireless Telegraphy Co.; The Temperley Transporter
Co.; Messrs. de Dion, Bouton and Co.; Messrs. Merryweather and Sons;
Mr. A. Crosby Lockwood; Mr. Dan Albone; Mr. J. B. Diplock; Mr. W.
H. Oatway; The National Cash Register Co.; The Wenzel Sculpturing
Machine Co.; Mr. E. W. Gaz; Sir W. G. Armstrong, Whitworth and Co.; The
International Harvester Co. and Messrs. Gwynne and Co.
TABLE OF CONTENTS
PAGE
INTRODUCTION v
AUTHOR'S NOTE xi
CHAPTER I
DELICATE INSTRUMENTS--WATCHES AND CHRONOMETERS--THE
MICROTOME--THE DIVIDING ENGINE--MEASURING MACHINES 17
CHAPTER II
CALCULATING MACHINES 42
CHAPTER III
WORKSHOP MACHINERY--THE LATHE--PLANING MACHINES--THE
STEAM HAMMER--HYDRAULIC TOOLS--ELECTRICAL TOOLS IN THE
SHIPYARD 59
CHAPTER IV
PORTABLE TOOLS 90
CHAPTER V
THE PEDRAIL: A WALKING STEAM-ENGINE 97
CHAPTER VI
INTERNAL COMBUSTION ENGINES--OIL ENGINES--ENGINES WORKED
WITH PRODUCER GAS--BLAST FURNACE GAS ENGINES 112
CHAPTER VII
MOTOR-CARS--THE MOTOR OMNIBUS--RAILWAY MOTOR-CARS 130
CHAPTER VIII
THE MOTOR AFLOAT--PLEASURE BOATS--MOTOR LIFEBOATS--MOTOR
FISHING BOATS--A MOTOR FIRE FLOAT--THE MECHANISM OF
THE MOTOR BOAT--THE TWO-STROKE MOTOR--MOTOR BOATS FOR
THE NAVY 150
CHAPTER IX
THE MOTOR CYCLE 175
CHAPTER X
FIRE ENGINES 185
CHAPTER XI
FIRE-ALARMS AND AUTOMATIC FIRE EXTINGUISHERS 191
CHAPTER XII
THE MACHINERY OF A SHIP--THE REVERSING ENGINE--MARINE
ENGINE SPEED GOVERNORS--THE STEERING ENGINE--BLOWING
AND VENTILATING APPARATUS--PUMPS--FEED HEATERS--FEED-WATER
FILTERS--DISTILLERS--REFRIGERATORS--THE
SEARCH-LIGHT--WIRELESS TELEGRAPHY INSTRUMENTS--SAFETY
DEVICES--THE TRANSMISSION OF POWER ON A SHIP 203
CHAPTER XIII
"THE NURSE OF THE NAVY" 236
CHAPTER XIV
THE MECHANISM OF DIVING 240
CHAPTER XV
APPARATUS FOR RAISING SUNKEN SHIPS AND TREASURE 248
CHAPTER XVI
THE HANDLING OF GRAIN--THE ELEVATOR--THE SUCTION
PNEUMATIC GRAIN-LIFTER--THE PNEUMATIC BLAST
GRAIN-LIFTER--THE COMBINED SYSTEM 252
CHAPTER XVII
MECHANICAL TRANSPORTERS AND
CONVEYERS--ROPEWAYS--CABLEWAYS--TELPHERAGE--COALING
WARSHIPS AT SEA 258
CHAPTER XVIII
AUTOMATIC WEIGHERS 274
CHAPTER XIX
TRANSPORTER BRIDGES 277
CHAPTER XX
BOAT- AND SHIP-RAISING LIFTS 283
CHAPTER XXI
A SELF-MOVING STAIRCASE 295
CHAPTER XXII
PNEUMATIC MAIL TUBES 301
CHAPTER XXIII
AN ELECTRIC POSTAL SYSTEM 315
CHAPTER XXIV
AGRICULTURAL MACHINERY--PLOUGHS--DRILLS AND SEEDERS--REAPING
MACHINES--THRESHING MACHINES--PETROL-DRIVEN FIELD
MACHINERY--ELECTRICAL FARMING MACHINERY 318
CHAPTER XXV
DAIRY MACHINERY--MILKING MACHINES--CREAM SEPARATORS--A
MACHINE FOR DRYING MILK 330
CHAPTER XXVI
SCULPTURING MACHINES 335
CHAPTER XXVII
AN AUTOMATIC RIFLE--A BALL-BEARING RIFLE 345
LIST OF ILLUSTRATIONS
PAGE
A CARVING MACHINE _Frontispiece_
MEASURING MACHINES 34
A CASH REGISTER 45
LATHE TURNING A BIG GUN 59
LATHE FOR BORING 16-INCH GUN 65
A STEAM HAMMER 72
A HUGE HYDRAULIC PRESS 82
A PEDRAIL TRACTION ENGINE 108
GREAT GAS ENGINE FOR BLAST FURNACES 128
MOTOR-CAR AND MOTOR-BOAT 151
A MOTOGODILLE 156
A MOTOR LAWN MOWER 182
UP-TO-DATE FIRE BRIGADE ENGINES 186
HOISTING A HEAVY GUN ON BOARD MAN-OF-WAR 204
FIXING A RAM TO A BATTLESHIP 228
A TRIPOD CRANE 237
MODERN DIVING APPARATUS 245
COALING AT SEA 271
A TRANSPORTER BRIDGE AT BIZERTA 278
A CANAL LIFT 289
AN AMERICAN CUTTER AND BINDER 322
A MOTOR PLOUGH 327
GIRL CARVING BY MACHINERY 343
THE REXER GUN 352
THE ROMANCE OF MODERN MECHANISM
CHAPTER I
DELICATE INSTRUMENTS
WATCHES AND CHRONOMETERS--THE MICROTOME--THE DIVIDING ENGINE--MEASURING
MACHINES
Owing to the universal use of watches, resulting from their cheapness,
the possessor of a pocket timepiece soon ceases to take a pride in the
delicate mechanism which at first added an inch or two to his stature.
At night it is wound up mechanically, and thrust under the pillow, to
be safe from imaginary burglars and handy when the morning comes. The
awakened sleeper feels small gratitude to his faithful little servant,
which all night long has been beating out the seconds so that its
master may know just where he is with regard to "the enemy" on the
morrow. At last a hand is slipped under the feather-bag, and the watch
is dragged from its snug hiding-place. "Bother it," says the sleepy
owner, "half-past eight; ought to have been up an hour ago!" and out he
tumbles. Dressing concluded, the watch passes to its day quarters in a
darksome waistcoat pocket, to be hauled out many times for its opinion
to be taken.
The real usefulness of a watch is best learnt by being without one
for a day or two. There are plenty of clocks about, but not always in
sight; and one gradually experiences a mild irritation at having to
step round the corner to find out what the hands are doing.
A truly wonderful piece of machinery is a watch--even a cheap one.
An expensive, high-class article is worthy of our admiration and
respect. Here is one that has been in constant use for fifty years.
Twice a second its little balance-wheel revolves on its jewelled
bearings. Allowing a few days for repairs, we find by calculation that
the watch has made no less than three thousand million movements in
the half-century! And still it goes ticking on, ready to do another
fifty years' work. How beautifully tempered must be the springs and
the steel faces which are constantly rubbing against jewel or metal!
How perfectly cut the teeth which have engaged one another times
innumerable without showing appreciable wear!
The chief value of a good watch lies in its accuracy as a time-keeper.
It is, of course, easy to correct it by standard clocks in the railway
stations or public buildings; but one may forget to do this, and in a
week or two a loss of a few minutes may lead to one missing a train, or
being late for an important engagement. Happy, therefore, is the man
who, having set his watch to "London time," can rely on its not varying
from accuracy a minute in a week--a feat achieved by many watches.
The old-fashioned watch was a bulky affair, protected by an outer
case of ample proportions. From year to year the size has gradually
diminished, until we can now purchase a reliable article no thicker
than a five-shilling piece, which will not offend the most fastidious
dandy by disarranging the fit of his clothes. Into the space of a small
fraction of an inch is crowded all the usual mechanism, reduced to
the utmost fineness. Watches have even been constructed small enough
to form part of a ring or earring, without losing their time-keeping
properties.
For practical purposes, however, it is advantageous to have a timepiece
of as large a size as may be convenient, since the difficulties of
adjustment and repair increase with decreasing proportions. The ship's
chronometer, therefore, though of watch construction, is a big affair
as compared with the pocket timepiece; for above all things it must be
accurate.
The need for this arises from the fact that nautical reckonings made by
the observation of the heavenly bodies include an element of _time_. We
will suppose a vessel to be at sea out of sight of land. The captain,
by referring to the dial of the "mechanical log," towed astern, can
reckon pretty accurately how _far_ the vessel has travelled since it
left port; but owing to winds and currents he is not certain of the
position on the globe's surface at which his ship has arrived. To
locate this exactly he must learn (a) his longitude, _i.e._ distance
E. or W. of Greenwich, (b) his latitude, _i.e._ distance N. or S.
of the Equator. Therefore, when noon approaches, his chronometers
and sextant are got out, and at the moment when the sun crosses the
meridian the time is taken. If this moment happens to coincide with
four o'clock on the chronometers he is as far west of Greenwich as
is represented by four twenty-fourths of the 360° into which the
earth's circumference is divided; that is, he is in longitude 60° W.
The sextant gives him the angle made by a line drawn to the sun with
another drawn to the horizon, and from that he calculates his latitude.
Then he adjourns to the chart-room, where, by finding the point at
which the lines of longitude and latitude intersect, he establishes his
exact position also.
When the ship leaves England the chronometer is set by Greenwich time,
and is never touched afterwards except to be wound once a day. In order
that any error may be reduced to a minimum a merchant ship carries at
least two chronometers, a man-of-war at least three, and a surveying
vessel as many as a dozen. The average reading of the chronometers is
taken to work by.
Taking the case of a single chronometer, it has often to be relied on
for months at a time, and during that period has probably to encounter
many changes of temperature. If it gains or loses from day to day, and
that _consistently_, it may still be accounted reliable, as the amount
of error will be allowed for in all calculations. But should it gain
one day and lose another, the accumulated errors would, on a voyage
of several months, become so considerable as to imperil seriously the
safety of the vessel if navigating dangerous waters.
As long ago as 1714 the English Government recognised the importance of
a really reliable chronometer, and in that year passed an Act offering
rewards of £10,000, £15,000, and £20,000 to anybody who should produce
a chronometer that would fix longitude within sixty, forty, and thirty
miles respectively of accuracy. John Harrison, the son of a Yorkshire
carpenter, who had already invented the ingenious "gridiron pendulum"
for compensating clocks, took up the challenge. By 1761 he had made a
chronometer of so perfect a nature that during a voyage to Jamaica that
year, and back the next, it lost only 1 min. 54-1/2 sec. As this would
enable a captain to find his longitude within eighteen miles in the
latitude of Greenwich, Harrison claimed, and ultimately received, the
maximum reward.
It was not till nearly a century later that Thomas Earnshaw produced
the "compensation balance," now generally used on chronometers and
high-class watches. In cheap watches the balance is usually a little
three-spoked wheel, which at every tick revolves part of a turn and
then flies back again. This will not suffice for very accurate work,
because the "moment of inertia" varies at different temperatures. To
explain this term let us suppose that a man has a pound of metal to
make into a wheel. If the wheel be of small diameter, you will be able
to turn it first one way and then the other on its axle quite easily.
But should it be melted down and remade into a wheel of four times
the diameter, with the same amount of metal as before in the rim, the
difficulty of suddenly reversing its motion will be much increased.
The weight is the same, but the speed of the rim, and consequently
its momentum, is greater. It is evident from this that, if a wheel
of certain size be driven by a spring of constant strength, its
oscillations will be equal in time; but if a rise of temperature should
lengthen the spokes the speed would fall, because the spring would
have more work to do; and, conversely, with a fall of temperature the
speed would rise. Earnshaw's problem was to construct a balance wheel
that should be able to keep its "moment of inertia" constant under all
circumstances. He therefore used only two spokes to his wheel, and to
the outer extremity of each attached an almost complete semicircle of
rim, one end being attached to the spoke, the other all but meeting the
other spoke. The rim-pieces were built up of an outer strip of brass,
and an inner strip of steel welded together. Brass expands more rapidly
than steel, with the result that a bar compounded of these two metals
would, when heated, bend towards the hollow side. To the rim-pieces
were attached sliding weights, adjustable to the position found by
experiment to give the best results.
We can now follow the action of the balance wheel. It runs perfectly
correctly at, say, a temperature of 60°. Hold it over a candle. The
spokes lengthen, and carry the rim-pieces _outwards_ at their fixed
ends; but, as the pieces themselves bend inwards at their free ends,
the balance is restored. If the balance were placed in a refrigerating
machine, the spokes would shorten, but the rim-pieces would bend
outwards.
As a matter of fact, the "moment of inertia" cannot be kept quite
constant by this method, because the variation of expansion is more
rapid in cold than in heat; so that, though a balance might be quite
reliable between 60° and 100°, it would fail between 30° and 60°.
So the makers fit their balances with what is called a _secondary_
compensation, the effect of which is to act more quickly in high
than in low temperatures. This could not well be explained without
diagrams, so a mere mention must suffice.
Another detail of chronometer making which requires very careful
treatment is the method of transmitting power from the main spring
to the works. As the spring uncoils, its power must decrease, and
this loss must be counterbalanced somehow. This is managed by using
the "drum and fusee" action, which may be seen in some clocks and in
many old watches. The drum is cylindrical, and contains the spring.
The fusee is a tapering shaft, in which a spiral groove has been cut
from end to end. A very fine chain connects the two parts. The key is
applied to the fusee, and the chain is wound off the drum on to the
larger end of the fusee first. By the time that the spring has been
fully wound, the chain has reached the fusee's smaller extremity. If
the fusee has been turned to the correct taper, the driving power
of the spring will remain constant as it unwinds, for it gets least
leverage over the fusee when it is strongest, and most when it is
weakest, the intermediate stages being properly proportioned. To test
this, a weighted lever is attached to the key spindle, with the weight
so adjusted that the fully wound spring has just sufficient power to
lift it over the topmost point of a revolution. It is then allowed a
second turn, but if the weight now proves excessive something must be
wrong, and the fusee needs its diameter reducing at that point. So the
test goes on from turn to turn, and alterations are made until every
revolution is managed with exactly the same ease.
The complete chronometer is sent to Greenwich observatory to be tested
against the Standard Clock, which, at 10 a.m., flashes the hour to
other clocks all over Great Britain. In a special room set apart for
the purpose are hundreds of instruments, some hanging up, others
lying flat. Assistants make their rounds, noting the errors on each.
The temperature test is then applied in special ovens, and finally
the article goes back to the maker with a certificate setting forth
its performances under different conditions. If the error has been
consistent the instrument is sold, the buyer being informed exactly
what to allow for each day's error. At the end of the voyage he brings
his chronometer to be tested again, and, if necessary, put right.
Here are the actual variations of a chronometer during a nineteen-day
test, before being used:--
Gain in _tenths_
Day. of seconds.
1st 1/2
2nd 3
3rd 4
4th 4
5th 1/2
6th 3
7th 0
8th 0
9th 4-1/2
10th 3
11th 4
12th 3
13th 3
14th 4
15th 5
16th 2
17th 3
18th 5
19th 1
An average gain of just over one quarter of a second per diem! Quite
extraordinary feats of time-keeping have been recorded of chronometers
on long voyages. Thus a chronometer which had been to Australia _viâ_
the Cape and back _viâ_ the Red Sea was only fifteen seconds "out";
and the _Encyclopædia Britannica_ quotes the performance of the three
instruments of S.S. _Orellana_, which between them accumulated an error
of but 2·3 seconds during a sixty-three-day trip.
An instrument which will cut a blood corpuscle into several
parts--that's the MICROTOME, the "small-cutter," as the name implies.
For the examination of animal tissues it is necessary that they should
be sliced very fine before they are subjected to the microscope.
Perhaps a tiny muscle is being investigated and cross sections of it
are needed. Well, one cannot pick up the muscle and cut slices off it
as you would off a German sausage. To begin with, it is difficult even
to pick the object up; and even if pieces one-hundredth of an inch long
were detached they would still be far too large for examination.
So, as is usually the case when our unaided powers prove unequal to
a task, we have recourse to a machine. There are several types of
microtomes, each preferable for certain purposes. But as in ordinary
laboratory work the Cambridge Rocking Microtome is used, let us give
our special attention to this particular instrument. It is mounted
on a strong cast-iron bed, a foot or so in length and four to five
inches wide. Towards one end rise a couple of supports terminating in
knife-edges, which carry a cross-bar, itself provided with knife-edges
top and bottom, those on the top supporting a second transverse bar.
Both bars have a long leg at right angles, giving them the appearance
of two large T's superimposed one on the other; but the top T is
converted into a cross by a fourth member--a sliding tube which
projects forward towards a frame in which is clamped a razor, edge
upwards.
The tail of the lower T terminates in a circular disc, pierced with
a hole to accommodate the end of a vertical screw, which has a large
circular head with milled edges. The upper T is rocked up and down
by a cord and spring, the handle actuating the cord also shifting on
the milled screw-head a very small distance every time it is rocked
backwards and forwards. As the screw turns, it gradually raises the
tail of the lower member, and by giving its cross-bar a tilt brings the
tube of the upper member appreciably nearer the razor. The amount of
twist given to the screw at each stroke can be easily regulated by a
small catch.
When the microscopist wishes to cut sections he first mounts his object
in a lump of hard paraffin wax, coated with softer wax. The whole is
stuck on to the face of the tube, so as to be just clear of the razor.
The operator then seizes the handle and works it rapidly until the
first slice is detached by the razor. Successive slices are stuck
together by their soft edges so as to form a continuous ribbon of wax,
which can be picked up easily and laid on a glass slide. The slide is
then warmed to melt the paraffin, which is dissolved away by alcohol,
leaving the atoms of tissue untouched. These, after being stained with
some suitable medium, are ready for the microscope.
A skilful user can, under favourable conditions, cut slices _one
twenty-five thousandth_ of an inch thick. To gather some idea of what
this means we will imagine that a cucumber one foot long and one and
a-half inches in diameter is passed through this wonderful guillotine.
It would require no less than 700 dinner-plates nine inches across to
spread the pieces on! If the slices were one-eighth of an inch thick,
the cucumber, to keep a proportionate total size, would be 260 feet
long. After considering these figures we shall lose some of the respect
we hitherto felt for the men who cut the ham to put inside luncheon-bar
sandwiches.
In the preceding pages frequent reference has been made to index
screws, exactly graduated to a convenient number of divisions. When
such screws have to be manufactured in quantities it would be far too
expensive a matter to measure each one separately. Therefore machinery,
itself very carefully graduated, is used to enable a workman to
transfer measurements to a disc of metal.
If the index-circle of an astronomical telescope--to take an
instance--has to be divided, it is centred on a large horizontal disc,
the circumference of which has been indented with a large number of
teeth. A worm-screw engages these teeth tangentially (_i.e._ at right
angles to a line drawn from the centre of the plate to the point
of engagement). On the shaft of the screw is a ratchet pinion, in
principle the same as the bicycle free-wheel, which, when turned one
way, also twists the screw, but has no effect on it when turned the
other way. Stops are put on the screw, so that it shall rotate the
large disc only the distance required between any two graduations. The
divisions are scribed on the index-circle by a knife attached to a
carriage over and parallel to the disc. The DIVIDING ENGINE used for
the graduation of certain astronomical instruments probably constitutes
the most perfect machine ever made. In an address to the Institution
of Mechanical Engineers,[1] the President, Mr. William Henry Maw, used
the following words: "The most recently constructed machine of the kind
of which I am aware--namely, one made by Messrs. Warner and Swasey, of
Cleveland, U.S.A.--is capable of automatically cutting the graduations
of a circle with an error in position not exceeding one second of arc.
(A second of an arc is approximately the angle subtended by a halfpenny
at a distance of three miles.) This means that on a 20-inch circle the
error in position of any one graduation shall not exceed 1/20,000 inch.
Now, the finest line which would be of any service for reading purposes
on such a circle would probably have a width equal to quite ten seconds
of arc; and it follows that the minute V-shaped cut forming this line
must be so absolutely symmetrical with its centre line throughout its
length, that the position of this centre may be determined within the
limit of error just stated by observations of its edges, made by aid of
the reading micrometer and microscope. I may say that after the machine
just mentioned had been made, it took _over a year's hard work_ to
reduce the maximum error in its graduations from one and a-half to one
second of arc."
The same address contains a reference to the great Yerkes telescope,
which though irrelevant to our present chapter, affords so interesting
an example of modern mechanical perfection that it deserves parenthetic
mention.
The diameter of a star of the seventh magnitude as it appears in
the focus of this huge telescope is 1/2,500 inch. The spiders' webs
stretched across the object glass are about 1/6,000 inch in diameter.
"The problem thus is," says Mr. Maw, "to move this twenty-two ton mass
(the telescope) with such steadiness in opposition to the motion of the
earth, that a star disc 1/2,500 inch in diameter can be kept threaded,
as it were, upon a spider's web 1/6,000 inch in diameter, carried at a
radius of thirty-two feet from the centre of motion. I think that you
will agree that this is a problem in mechanical engineering demanding
no slight skill to solve; but it has been solved, and with the most
satisfactory results." The motions are controlled electrically; and
respecting them Professor Barnard, one of the chief observers with this
telescope, some time ago wrote as follows: "It is astonishing to see
with what perfect instantaneousness the clock takes up the tube. The
electric slow motions are controlled from the eye end. So exact are
they that a star can be brought from the edge of the field and stopped
instantaneously behind the micrometer wire."
Dividing engines are used for ruling parallel lines on glass and
metal, to aid in the measurements of microscopical objects or the
wave-lengths of light. A _diffraction grating_, used for measuring the
latter, has the lines so close together that they would be visible
only under a powerful microscope. Glass being too brittle, a special
alloy of so-called _speculum_ metal is fashioned into a highly polished
plate, and this is placed in the machine. A delicate screw arrangement
gradually feeds the plate forwards under the diamond point, which is
automatically drawn across the plate between every two movements.
Professor H. A. Rowlands has constructed a parallel dividing engine
which has ruled as many as 120,000 lines to the inch. To get a
conception of these figures we must once again resort to comparison.
Let us therefore take a furrow as a line, and imagine a ploughman going
up and down a field 120,000 times. If each furrow be eight inches
wide, the field would require a breadth of nearly _fourteen miles_ to
accommodate all the furrows! Again, supposing that a plate six inches
square were being ruled, the lines placed end to end would extend for
seventy miles!
Professor Rowlands' machine does the finest work of this kind. Another
very perfect instrument has been built by Lord Blythswood, and as some
particulars of it have been kindly supplied, they may fitly be appended.
If a first-class draughtsman were asked how many parallel straight
lines he would rule within the space of one inch, it is doubtful
whether he would undertake more than 150 to 200 lines. Lord
Blythswood's machine can rule fourteen parallel lines on a space
equivalent to the _edge_ of the finest tissue paper. So delicate are
the movements of the machine that it must be protected from variations
of temperature, which would contract or expand its parts; so the room
in which it stands is kept at an even heat by automatic apparatus, and
to make things doubly sure the engine is further sheltered in a large
case having double walls inter-packed with cotton wool.
In constructing the machine it was found impossible, with the most
scientific tools, to cut a toothed wheel sufficiently accurate to drive
the mechanism, but the errors discovered by microscopes were made good
by the invention of a small electro-plating brush, which added the
thinnest imaginable layer of metal to any tooth found deficient.
During the process of ruling a grating of only a few square inches
area, the machine must be left severely alone in its closed case. The
slightest jar would cause unparallelism of a few lines, and the ruin of
the whole grating. So for several days the diamond point has its own
way, moving backwards and forwards unceasingly over the hard metal, in
which it chases tiny grooves. At the end the plate has the appearance
of mother-of-pearl, which is, in fact, one of nature's diffraction
gratings, breaking up white light into the colours of the spectrum.
You will be able to understand that these mechanical gratings are
expensive articles. Sometimes the diamond point breaks half-way through
the ruling, and a week's work is spoilt. Also the creation of a
reliable machine is a very tedious business. Ten pounds per square inch
of grating is a low price to pay.
The greatest difficulty met with in the manufacture of the dividing
engine is that of obtaining a mathematically correct screw. Turning
on a lathe produces a very rough spiral, judged scientifically. Some
threads will be deeper than others, and differently spaced. The screw
must, therefore, be ground with emery and oil introduced between it
and a long nut which is made in four segments, and provided with
collars for tightening it up against the screw. Perhaps a fortnight
may be expended over the grinding. Then the screw must undergo rigid
tests, a nut must be made for it, and it has to be mounted in proper
bearings. The explanation of the method of eliminating errors being
very technical, it is omitted; but an idea of the care required may be
gleaned from Professor Rowlands' statement that an uncorrected error of
1/300,000 of an inch is quite sufficient to ruin a grating!
In the Houses of Parliament there is kept at an even temperature a
bronze rod, thirty-eight inches long and an inch square in section.
Near the ends are two wells, rather more than half an inch deep, and at
the bottom of the wells are gold studs, each engraved with a delicate
cross line on their polished surfaces. The distance between the lines
is the imperial yard of thirty-six inches.
The bar was made in 1844 to replace the Standard destroyed in 1834,
when both Houses of Parliament were burned. The original Standard was
the work of Bird, who produced it in 1760. In June, 1824, an Act had
been passed legalising this Standard. It says:--
"The same Straight Line or Distance between the Centers of the said Two
Points in the said Gold Studs in the said Brass Rod, the Brass being at
the temperature of Sixty-two Degrees by Fahrenheit's Thermometer, shall
be and is hereby denominated the 'Imperial Standard Yard.'"
To provide for accidents to the bar, the Act continues: "And whereas
it is expedient that the said Standard Yard, if lost, destroyed,
defaced, or otherwise injured, should be restored to the same Length by
reference to some invariable natural Standard: And whereas it has been
ascertained by the Commissioners appointed by His Majesty to inquire
into the subject of Weights and Measures, that the Yard hereby declared
to be the Imperial Standard Yard, when compared with a Pendulum
vibrating Seconds of Mean Time in the Latitude of London in a Vacuum
at the Level of the Sea, is in the proportion of Thirty-six Inches to
Thirty-nine Inches and one thousand three hundred and ninety-three
ten-thousandth Parts of an Inch."
The new bar was made, however, not by this method, but by comparing
several copies of the original and striking their average length. Four
accurate duplicates of the new standard were secured, one of which
is kept in the Mint, one in the charge of the Royal Society, one at
Westminster Palace, and the fourth at the Royal Observatory, Greenwich.
In addition, forty copies were distributed among the various foreign
governments, all of the same metal as the original.
The French metre has also been standardised, being equal to one
ten-millionth part of a quadrant of the earth's meridian (_i.e._ of
the distance from the Equator to either of the Poles), that is, to
39·370788 inches. Professor A. A. Michelson has shown that any standard
of length may be restored by reference to the measurement of wave
lengths of light, with an error not exceeding one ten-millionth part of
the whole.
It might be asked "Why should standards of such great accuracy be
required?" In rough work, such as carpentry, it does not, indeed,
matter if measurements are the hundredth of an inch or so out. But when
we have to deal with scientific instruments, telescopes, measuring
machines, engines for dividing distances on a scale, or even with
metal turning, the utmost accuracy becomes needful; and a number of
instruments will be much more alike in all dimensions if compared
individually with a common standard than if they were only compared
with one another. Supposing, for instance, a bar of exact diameter is
copied; the copy itself copied; and so on a dozen times; the last will
probably vary considerably from the correct measurements.
Hence it became necessary to standardise the foot and the inch by
accurate subdivisions of the yard. This was accomplished by Sir Joseph
Whitworth, who in 1834 obtained two standard yards in the form of
measure bars, and by the aid of microscopes transferred the distance
between the engraved lines to a rectangular _end_-measure bar, _i.e._
one of which the end faces are exactly a yard apart.
He next constructed his famous machine which is capable of detecting
length differences of _one millionth_ of an inch. Two bars are advanced
towards each other by screw gearing: one by a screw having twenty
threads to the inch, and carrying a graduated hand-wheel with 250
divisions on its rim; the other by a similar screw, itself driven by a
worm-screw, working on the rim, which carries 200 teeth. The worm-screw
has a hand-wheel with a micrometer graduation into 250 divisions of
its circumference. So that, if this be turned one division, the second
screw is turned only 1/250 × 1/200 of a division, and the bar it drives
advances only 1/20 × 1/200 × 1/250 = 1/1,000,000 of an inch. The screw
at the other end of the machine (which in appearance somewhat resembles
a metal lathe) is used for rapid adjustment only.
[Illustration: DELICATE MEASURING MACHINES
The upper illustration shows a Pratt-Whitney Measuring Machine in
operation to decide the thickness of a cigarette paper, which is
one-thousandth of an inch thick. This machine will measure variations
of length or thickness as minute as one hundredth-thousandth of an
inch. The lower illustration shows a Whitworth Measuring Machine which
is sensitive to variations of one-millionth of an inch.]
"He (Sir J. Whitworth) obtained the subdivision of the yard by making
three foot pieces as nearly alike as was possible, and working these
foot pieces down until each was equal to the others, and placing them
end to end in his millionth measuring machine; the total length of the
three foot pieces was then compared with a standard end-measure yard.
These three foot pieces were ground until they were exactly equal to
each other, and the three added together are equal to the standard
yard. The subdivision of the foot into inch pieces was made in the same
way."[2]
A doubt may have arisen in the reader's mind as to the possibility of
determining whether the measuring machine is screwed up to the exact
_tightness_. Would the measuring bars not compress a body a little
before it appeared tight? Workmen, when measuring a bar with callipers,
often judge by the sense of touch whether the jaws of the callipers
pass the bar with the proper amount of resistance; but when one has to
deal with millionths of an inch, such a method would not suffice. So
Sir Joseph Whitworth introduced a _feeling-piece_, or _gravity-piece_.
Mr. T. M. Goodeve thus describes it in _The Elements of Mechanism_:
The gravity-piece consists of a small plate of steel with parallel
plane sides, and having slender arms, one for its partial support, and
the other for resting on the finger of the observer. One arm of the
piece rests on a part of the bed of the machine, and the other arm is
tilted up by the forefinger of the operator. The plane surfaces are
then brought together, one on each side of the feeling-piece, until
the pressure of contact is sufficient to hold it supported just as it
remained when one end rested on the finger. This degree of tightness is
perfectly definite, and depends on the weight of the gravity-piece, but
not on the estimation of the observer.
In this way the expansion due to heat when a 36-inch bar has been
touched for an instant with the finger-nail may be detected.
One of the most beautiful measuring machines commercially used comes
from the factories of the Pratt-Whitney Co., Hartford, Connecticut,
the well-known makers of machine tools and gauges of all kinds. It
is made in different sizes, the largest admitting an 80-inch bar.
Variations of 1/100,000 of an inch are readily determined by the use of
this machine. It therefore serves for originating gauge sizes, or for
duplicating existing standards. The adjusting screw has fifty threads
to the inch, and its index-wheel is graduated to 400 divisions, giving
an advance of 1/20,000 inch for each division: while by estimation this
may be further subdivided to indicate one-half or even one-quarter of
this small amount. Delicacy of contact between the measuring faces is
obtained by the use of auxiliary jaws holding a small cylindrical gauge
by the pressure of a light helical spring which operates the sliding
spindle to which one of these auxiliary jaws is attached.
On one side of the "head" of the machine is a vertical microscope
directed downwards on to a bar on the bed-plate, in which are a number
of polished steel plugs graved with very fine central cross lines, each
exactly an inch distant from either of its neighbours. A cross wire in
the microscope tells when it is accurately abreast of the line below
it. Supposing, then, that a standard bar three inches in diameter has
to be tested. The "head" is slid along until the microscope is exactly
over the "zero" plug line, and the divided index-wheel is turned
until the two jaws press each other with the minimum force that will
hold up the feeling-piece. Then the head is moved back and centred
on the 3-inch line, and the bar to be tested is passed between the
jaws. If the feeling-piece drops out it is too large, and the wheel
is turned back until the jaws have been opened enough to let the bar
through without making the feeling-piece fall. An examination of the
index-wheel shows in hundred-thousandths of an inch what the excess
diameter is.
On the other hand, if the bar were too small, the jaws would need to be
closed a trifle: this amount being similarly reckoned.
We have now got into a region of very "practical politics," namely,
the subject of _gauges_. All large engineering works which turn out
machinery with interchangeable parts, _e.g._ screws and nuts, must keep
their dimensions very constant if purchasers are not to be disgusted
and disappointed. The small motor machinery so much in evidence to-day
demands that errors should be kept within the ten-thousandth of an
inch. An engineer therefore possesses a set of standard gauges to test
the diameter and pitch of his screw threads and nuts; the size of
tubes, wires; the circumference of wheels, etc.
Great inconvenience having been experienced by American railroad-car
builders on account of the varying sizes of the screws and bolts which
were used on the different tracks--though all were supposed to be of
standard dimensions--the masters determined to put things right; and
accordingly Professors Roger and Bond and the Pratt-Whitney Co. were
engaged to work in collaboration in connection with the manufacture of
tools for minute measurements, viz. to 1/50,000 inch. "To give an idea
of what is implied by this, let it be supposed that a person should
take a pair of dividing compasses and lay off 50,000 prick-marks 1/8
inch apart in a straight line. To do this the line would require to
be over 520 feet, or nearly a tenth of a mile long. Imagine that many
prick-marks compressed into the space of an inch, and you have an
imperfect idea of the minuteness of the measurements which can now be
made by the Pratt and Whitney Co."[3]
The standard taps and dies were supplied to tool-makers and engineers,
who could thus determine whether articles supplied to them were of the
proper dimensions. Nothing more was then heard of nuts being a "trifle
small" or bolts "a leetle large." And so beautifully tempered were the
dies made from the standards that one manufacturer claimed to have cut
18,800 cold-pressed nuts without any difference being perceptible in
their sizes.
To appreciate what the difference of a thousandth of an inch makes in a
true fit, you should handle a set of plug and ring gauges; the ring a
true half-inch internally, the plugs half-inch, half an inch less one
ten-thousandth of an inch, and half an inch less one-thousandth, in
diameter.
The true half-inch plug needs to be forcibly driven into the ring on
account of the friction between the surfaces. The next, if oiled, will
slide in quite easily, but if left stationary a moment will "seize,"
and have to be driven out. The third will wobble very perceptibly, and
would be at once discarded by a good workman as a bad fit.
For extremely accurate measurements of rods, calliper gauges, shaped
somewhat like the letter Y, are used, the horns terminating in polished
parallel jaws. Such a gauge will detect a difference of 1/20,000 inch
quite easily.
So accurately can plug gauges be made by reference to a measuring
machine, that a gold leaf 1/30,000 inch thick would be three times too
thick to insert between the gauge and the jaws of the machine!
You must remember that in high-class workmanship these gauges are
constantly being used. As time goes on, the "limit of error" allowed
in many classes of machine parts is gradually lessened, which shows
the simultaneous improvement of all machinery used in the handling
of metal. James Watt was terribly hampered, when developing his
steam-engine, by the difficulty of procuring a true cylinder for his
pistons to work in with any approach to steam-tightness. His first
cylinder was made by a smith of hammered iron soldered together. The
next was cast and bored, but stuffing it with paper, cork, putty,
pasteboard, and "old hat" proved useless to stem the leakage of steam.
No wonder, considering that the finished cylinder was one-eighth of
an inch larger in diameter at one end than at the other. Watt was in
advance of his time. Neither machinery nor workmanship had progressed
sufficiently to meet the requirements of the steam-engine. To-day
an engineer would confidently undertake to bore a cylinder five
feet in diameter with a variation from truth of not more than one
five-hundredth of an inch.
Before passing from the subject of measuring machines, which play
so important a part in modern mechanism, we may just glance at the
electrical method of Dr. P. E. Shaw. He discovered recently that two
clean metal surfaces can, by means of an electric current, feel one
another on touching with a delicacy that far transcends that of the
purely mechanical machine. The mechanism he employs is thus devised: A
finely cut vertical screw having fifty threads to the inch has a disc
graduated into 500 parts. The screw can be turned by means of a pulley
string from a distance, and it is thus possible to give the top end of
the screw a movement of 1/25,000 inch, when a movement corresponding to
one graduation is made.
This small movement is reduced by a train of six levers, the long arm
of each bearing on the short arm of the one before it. The movement of
the last lever of the train is thus reduced to 1/4,000 of that of the
screw point, so a movement of 1/4,000 × 1/25,000 inch = 1/100,000,000
inch is obtained!
How can such a movement be judged? A telephone and voltaic cell are
joined to the last lever of the train and to the object whose movement
is under examination. If they touch, the telephone sounds. An observer
listens in the telephone, and if the object moves for any reason he can
find out how much it moves by turning the screw until contact is made
again.
Out of the many applications of this apparatus three may be given.
(1) A short bar of iron when magnetised elongates about 1/1,000,000
of its length. If further magnetised it contracts. These changes can
readily be measured with the instrument.
(2) The smallest sound audible in the telephone is due to a movement
of the diaphragm of the telephone by about 1/50,000,000 of an inch.
This has been actually measured by Dr. Shaw and is by far the smallest
distance ever directly recorded. It is about twice the diameter of the
molecules of matter.
(3) Dispensing with levers, the screw alone is used for rougher work.
Dr. Shaw has shown that one hundred-thousandth of an inch is the
smallest dimension visible under a microscope. By fitting an electric
measuring apparatus to the microscope carriage it becomes quite easy
to measure minute distances. The microscope contains a cross wire
which, when the object has been laid on the microscope stage, is
centred on one side of the object. The electric contact screw is then
advanced till it makes contact with the stage and a sound arises in
the telephone. A reading of the screw disc having been taken, the
screw is drawn in and the microscope stage is traversed sufficiently
to bring the wire in line with the other side of the object. Once more
the operator makes electrical contact and gets a second reading, the
difference between the two being the diameter of the object. In this
manner the bacillus of tuberculosis has been proved to have an average
diameter of 31/250,000 of an inch.
The same method is employed to gauge the distance between the lines on
a diffraction grating.
FOOTNOTES:
[1] April 19th, 1901.
[2] G. M. Bond in a lecture delivered before the Franklin Institute,
February 29th, 1884.
[3] _Report on Standard Screw Threads_, Philadelphia, 1884.