Mechanics E-Book

Alexander Russell Bond

• Herausgeber: Science & Technology Publishing
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 489

Veröffentlichungsjahr: 2025

Beschreibung

Mechanics: The Science of Machinery is a comprehensive and accessible treatise that delves into the fundamental principles and practical applications of mechanics, specifically as they relate to machinery and engineering. Authored by Alexander Blackie William Kennedy and Richard Shelldon, this classic work was originally published in the late 19th century as part of the Science for Beginners series, aiming to make the complex world of mechanical science understandable to a broad audience, including students, inventors, and general readers with an interest in technology. The book systematically explores the essential concepts of mechanics, beginning with the basic laws of motion, force, and energy, and gradually progressing to more advanced topics such as levers, pulleys, gears, and the transmission of power. Through clear explanations, detailed illustrations, and practical examples, the authors demystify the inner workings of machines, from the simplest tools to more intricate mechanical systems. The text covers the structure and function of various mechanical devices, the principles behind their operation, and the scientific laws that govern their behavior. Mechanics: The Science of Machinery stands out for its pedagogical approach, using everyday language and relatable analogies to explain technical concepts. The book is richly illustrated with diagrams and drawings that enhance understanding and provide visual context for the mechanical principles discussed. It also includes historical insights into the development of machinery, highlighting the ingenuity and creativity that have driven technological progress. Ideal for self-study or as a supplementary resource in educational settings, this book remains a valuable reference for anyone interested in the foundations of mechanical engineering, the evolution of machines, and the science that underpins the technology shaping our world. Whether you are a student, a hobbyist, or simply curious about how things work, Mechanics: The Science of Machinery offers a thorough and engaging exploration of the mechanical universe.

Leseprobe

Copyright, Ewing Galloway

The drop forge. A fourteen-ton hydraulic press is employed in forging an immense open hearth steel plate.

Popular Science Library

EDITOR-IN-CHIEF

GARRETT P. SERVISS

AUTHORS

WILLIAM J. MILLER HIPPOLYTE GRUENER A. RUSSELL BOND D. W. HERING LOOMIS HAVEMEYER ERNEST G. MARTIN ARTHUR SELWYN-BROWN ROBERT CHENAULT GIVLER ERNEST INGERSOLL WILFRED MASON BARTON WILLIAM B. SCOTT ERNEST J. STREUBEL NORMAN TAYLOR DAVID TODD CHARLES FITZHUGH TALMAN ROBIN BEACH

ARRANGED IN SIXTEEN VOLUMES WITH A HISTORY OF SCIENCE, GLOSSARIES AND A GENERAL INDEX

ILLUSTRATED

VOLUME FIVE

P. F. COLLIER & SON COMPANY

NEW YORK

Copyright 1922By P. F. Collier & Son Company

MANUFACTURED IN U. S. A.

MECHANICS

The Science of Machinery

BY

A. RUSSELL BOND

Formerly Managing Editor, Scientific American

P. F. COLLIER & SON COMPANY NEW YORK

PREFACE

ALTHOUGH strictly speaking the term “Mechanics” applies to that branch of Physics that deals with the actions of forces on material bodies, originally the word had a broader meaning embracing all machinery and mechanical inventions. To-day popular usage is restoring to the term its original broad interpretation, and it is in this popular but rather unorthodox sense that “Mechanics” has been chosen as the title of this book; for although certain elementary principles of mechanics are described and explained, the major portion of the book deals with machines and their evolution to their present stage of perfection.

Machines are man’s creation, and yet in a sense the man of to-day is a machine product; for modern civilization owes its material and in large measure its esthetic development to machinery. The story of machinery, from primitive man’s first attempts to augment his physical powers with mechanical aids down to the present era of gigantic, steel-muscled machinery and marvelously intricate mechanisms, is the story of human progress. It is this story that we have endeavored to tell in the following pages, but the subject is too large to be covered in a single volume or even a dozen volumes. Under the circumstances we have been obliged to confine ourselves to a mere outline, selecting certain avenues of progress more marked than others and presenting brief sketch maps of them. We have aimed in this way to give a bird’s-eye view of the whole story of human progress in things material.

The book has not been written for the mechanical engineer, but for the layman who would learn of the mechanical contrivances that contribute to his material welfare; hence technical terms have been avoided, as far as possible, and where unavoidable have been explained and defined.

A. Russell Bond

CONTENTS

CHAPTERPAGE I. Tool-Making Animals9 II. The Anatomy of a Machine20 III. Machines for Making Machines42 IV. Counting Seconds57 V. Putting Rivers to Work75 VI. Liquid Levers and Gears94 VII. Airvs.Water109 VIII. Air Springs and Cushions126 IX. Power from Heat139 X. Burning Fuel in the Engine Cylinder155 XI. When Coal and Oil Are Exhausted171 XII. Invasion of the Sea182 XIII. Sliding, Rolling, Walking, and Creeping203 XIV. Invasion of the Sky219 XV. Helping the Farmer239 XVI. Machining the Earth251 XVII. From Fiber to Fabric268 XVIII. The Making of Paper289 XIX. Typesetting and Printing Machinery300 XX. Cast Iron, Wrought Iron, and Steel314 XXI. Animated Machinery326 XXII. Heat Vacuums345 XXIII. Engines of Destruction359 XXIV. Summary of Mechanical Progress376

LIST OF ILLUSTRATIONS

The Drop Forge—Forging a Steel PlateFrontispieceFACING PAGERaising Water with a Chain of Pots—a Primitive Pump Used in Egypt32Horse-Operated Chain Pump Used in Greece32Multiple Spindle Drill in a Motor Car Factory33Bucket of a Giant Dredge with Its Jaws Wide Open64Gold Dredge Eating Its Way Through River Sands65Suction Dredge Excavating a Channel and Building New Land65Air Lock of a Pneumatic Caisson96Subaqueous Tunnel Showing the Shield in the Background97Wharf Protected by a Pneumatic Breakwater128Sun-Power Plant in Egypt129Close-Up of One of the Reflectors of a Sun-Power Plant129Giant Caproni Hydroaeroplane160Concrete Steamship “Faith”161“Virginian,” the Largest Locomotive in the World161Loom Provided with a Jacquard Attachment224Battery of Mule Spinning Frames225Jacquard Attachment for Loom225Digging a Trench with a Machine of the Chain Type256Multiple Plowing on a Western Wheat Field257Sawing Logs of Pulpwood into 16-Inch Lengths288Heater in a Pulp Mill Where the Wood Pulp Is Mixed with Clay288Modern Fourdrinier Paper-Making Machines289Molten Metal from a Blast Furnace320Bessemer Converter Blowing Air Through a Mass of Molten Iron320Steel Beam Passing Through the Finishing Rolls321Compositor at Work on a Linotype Machine352The Optophone, Which Enables the Blind to Read Print353Blind Man Reading with His Ears353

CHAPTER I

TOOL-MAKING ANIMALS

WHEN we review the marvelous achievements of modern civilization we are quite willing to agree with the ancient psalmist that man is “little lower than the angels.” But at the other end of the scale our complacency is liable to receive a rude shock; apparently the boundary between man and beast is not so very easy to draw.

We used to be told that one important superiority of mankind lies in the fact that he makes use of tools, while the beast never uses any implement except those that nature has furnished him as part of his own organism. But a gorilla will throw stones at his enemy; and he knows how to brandish a club and use it with telling force. Some of the apes are known to use sticks to knock down fruit which is out of the reach of their hands, and they will crack nuts with a stone. Clearly these animals are tool users. A very intelligent orang-utan in the Bronx Zoölogical Garden, New York, after trying for days to wrench off a bracket from the wall of his cage eventually used the horizontal bar of his trapeze as a lever and with it pried the offending bracket from its fastenings. Here was real invention and the discovery of the principle of leverage. The great black arara cockatoo of New Guinea uses his beak as a saw to weaken the shells of hard nuts, and to keep his bill from slipping off the smooth shell he is ingenious enough to wrap a leaf around the nut to hold it steady.

Even in the insect world we find creatures resourceful enough to make use of tools. Prof. Franz Doflein of the University of Breslau tells of an interesting study of certain ants, known as the Oecophylla smaragdina, who build their nests in bushes by fastening leaves together with fine threads. But the ants that build the nests cannot spin these threads, because they possess no spinning glands. They must depend upon their larvæ for this product. When a rent was made in one of these nests, a band of the tiny creatures ranged themselves side by side along the torn edge of the leaf and reached across the gap until they could catch hold of the opposite edge with their mandibles. Then they drew back step by step, with perfect teamwork, until the two edges were brought together. In the meantime, other ants had rushed to the nursery and each one had picked up a larva, not with the idea of bearing it off to safety, but in order that the babies might spin the thread which the adult ants were unable to do. The larvæ were carried to the breach in the nest and moved back and forth across the rent. They were pressed first against one side of the tear and then the other and all the while were squeezed tightly, evidently with the purpose of making them spin. Gradually a fine silky web was woven across the torn leaf and eventually the rent was completely patched.

Unquestionably these little ants are tool-using animals, because they make their larvæ serve as spinning spindles and also as weavers’ shuttles. However, this can hardly be cited as a point in common with even the lowest type of man, for the ants merely use the tools they find at their disposal. They certainly cannot be credited with having produced or even improved the tool which they use, whereas even in the most primitive of men we find that the tools used are not only carefully selected for the work to be performed, but are actually, shaped, be it ever so crudely, to suit the job.

Clearly we must shift the boundary between man and beast, distinguishing the former as the creature who artificially improves his tools. But even here it is not absolutely certain that the boundary will stand. Wilhelm Boelsche, a well-known German writer on natural history, calls attention to the “blacksmith woodpecker” which will thrust hard pine nuts into cracks in the trunk of a tree, so that they are held as if in a vise, enabling the bird to operate upon the seed more easily. Furthermore, this woodpecker will actually make a hole in the tree to receive the nut if there is not a hole or crack handy, so that evidently this animal does produce or artificially improve the tool that it uses.

There are a few such examples in nature, just enough to cast a bit of uncertainty on the boundary we have set. But although the actual line of demarcation may not be clear, there is no question but that the lowest type of humanity now existent, or of which we have any record, is or was a tool maker. Chipped stones evidently fashioned by man for some useful purpose are found even in the remains of the Middle Tertiary Epoch. The spirit of inquiry, of experiment, of invention, and the ambition to dominate over other members of the animal kingdom or over the obstacles imposed by nature, are to be found more or less active among all peoples, no matter how lowly a position they may occupy in the scale of civilization.

WAR AS A STIMULUS OF INVENTION

The most primitive implements were probably developed for the purpose of war. From the very earliest times, down to the present day, war has been a most potent stimulus of invention. The first tools ever used were probably intended to enable the user to cope with dangerous enemies. They marked the first stage in the conquest of brain over mere brawn. The primitive weapons were used not only in fighting other men, but in fighting off dangerous animals, and then in hunting animals for food. No doubt the first implement ever used was a club, which gave a real advantage over the unarmed, scratching, tearing, and biting enemy. This was a lever which increased the reach of the fighter, and also increased the power of his blow. The heavier the club, the more dangerous the weapon, particularly when most of the weight was centered at the outer end of the stick. But he was a real genius who first fastened a rock to the end of his club.

THE ART OF BREAKING STONES

Then arose the art of breaking stones—breaking them skillfully, so as to form a jagged cutting edge. When man began to fashion tools of stone he left imperishable records of his craftsmanship which enable us to trace his progress in invention. The first finished tool we find was the fist hatchet—a stone roughly chipped to form a cutting edge and of convenient shape for the grasp of the hand. This primitive tool very slowly, through a period covering thousands of years, developed into all manner of cutting implements, some with handles of wood and bone. The ax head was followed by the spearhead and this finally by the arrowhead, showing that man had at last found a mechanical substitute for his muscles to hurl projectiles farther and with greater accuracy than he could throw them by hand.

We marvel at the resourcefulness and skill of the primitive savage in working so difficult a material as stone. It would baffle a modern mechanic to be required to shape a piece of flint into an arrowhead with no other tool than a piece of bone. He is so accustomed to using tools which are harder than the material they are intended to shape that he cannot conceive of making any impression upon a piece of flint with a piece of bone, to say nothing of a stick of hard wood, and yet such tools were used away back in the Stone Age. At first stones were roughly shaped by hammering them together. Then the artisans became more skilled. They discovered that certain stones could be chipped more regularly and evenly, and the art of flaking off chips of flint sprang up. Some specimens that belonged to ages long preceding that of recorded history are beautifully done. The spearheads are symmetrically shaped like a long narrow leaf, and the stone is evenly furrowed on both sides with a keen edge all around.

Not only did primitive artisans shape the stone implements with hammer blows, but they learned how to shape stone by pressure as well, using a tool that was relatively soft. It is not a very difficult matter to shape even so hard a substance as glass merely by pressure. If a piece of glass is laid on a table with its edge slightly overhanging that of the table, it is possible to chip off the overhanging edge by pressing a nail or even a hard stick of wood against this edge. A small flake of glass is thus removed, and, by continuing the process, arrowheads of any shape may be formed. The tool is placed not against the upper surface of the glass, but against the edge of the glass, so that only the lower surface of it is split or flaked off. Then the glass is turned over and a chip is taken off the opposite face.

In the Middle Stone Age we find the primitive craftsman equipped with a very complete assortment of stone tools. He had hammers, chisels, scrapers, drills, and polishing tools. He knew how to make useful household implements, such as spoons and ladles, out of bone. He polished his work and ornamented the implements with carvings of animals. Ivory pins and needles show that he had begun to make himself clothing from the skins of animals and that he sewed them together with thongs or tendons.

In the Late Stone Age he had learned how to make vessels of fire-baked clay. His axes were ground to a sharp edge, and he bored holes in the ax head to receive the ax handle. The Swiss lake dwellers built houses of wood and fitted them with all sorts of wooden furniture carved with stone tools. Among the remains of these interesting settlements may be found balls of clay which, from the fact that one of them was discovered with a spool of flax still attached to it, were evidently used as spinning “whorls” used for spinning flax into thread. Clothing of skins was giving way to or being supplemented with clothing of woven fabric.

DISCOVERY OF THE LEVER AND THE WEDGE

Prior to the Stone Age the club was undoubtedly used, in time of peace—if there ever was a time of peace in those days—to batter down trees, to beat through entanglements and to dislodge great stones. Here the first idea of leverage was evidently employed. The club with a rock tied to it, particularly if the rock was shaped with a sharp edge, made a better implement for hewing trees. It is quite probable that soon after this stage of development had been reached, some one discovered the use of the wedge, particularly in splitting timber. Of course, no one realized in those early days why it was that he could pry up a greater weight with a lever than he could lift directly by hand, or why he could split open a log by driving wedges into it. The art of mechanics was in existence long ages before science of mechanics began to be studied. But it was not until men began to look into the why of things that rapid progress was made.

We can go on endlessly with our speculations on the evolution of tools and machinery up to the time when historians began to record the mechanical achievements of man. Unfortunately even after historians began to write they were so filled with admiration for the destructive work of man that they had no time to record his constructive work. The warrior who spread havoc and terror received all the glory, and his deeds were written on parchment, inscribed in clay and carved in stone; but the humble artisan was not worthy of mention. Even when the science of mechanics came to be studied, it was shrouded in a veil of mystery, and it was beneath the dignity of the man of science to impart his knowledge to the artisan. There was a lack of cooperation between science and industry that has persisted to a certain extent even up to the present time. Some of the most ingenious inventions of the ancients were employed by a corrupt and crafty priesthood to produce apparently miraculous effects and hoodwink the general public; and so, in looking back to the early days of mechanics, we are obliged to draw upon our imagination to trace its evolution, supplementing this by a study of the tools of primitive people of more recent time. Practically every form of hand tool we now use must have been known to the ancient artisan.

INVENTION OF THE WHEEL

We are not going to attempt to write a history of the evolution of machinery, but there is one invention whose origin is lost in the remote prehistoric ages which deserves more than passing attention. It is a pity that we have no clue as to who invented the wheel or how this most important element that enters into the construction of nearly all machinery was evolved. The invention called for a remarkable degree of originality. There is nothing like a wheel in nature. Levers we have in our own physical frame. But a wheel is something that is distinctly a human creation. Whoever invented it must have been a real genius, a James Watt or a Thomas Edison of his day. Certainly we owe more to the invention of the wheel than we do even to so revolutionary a machine as the steam engine, or the flying machine. How it was ever first conceived is a mystery. Maybe this primeval genius got his idea from seeing a stone rolling downhill, or he may have seen a tumbling weed rolling along the ground before the wind. It may be that the forerunner of the wheel was a roller shaped out of a log, for certainly primitive civilization must have advanced enough to have known how to hew timber before it would have been capable of fashioning a wheel. Some observant man might have noticed that he could drag a heavy timber over a rolling log much more easily than he could along the bare ground, and gradually the roller evolved into a wheel.

We can speculate upon the evolution of vehicles and transportation, once the wheel was invented. Of course, the first method of transporting loads was to carry them in the arms. Possibly loads were placed on skids and dragged along by one end. Away back in early times, it was discovered that two persons could carry more than twice as much as one, if the load were placed on a couple of poles. There was no friction to contend with, and not only was the load cut in two, because each man bore half of it, but the position of the load was such that it could be borne more easily. After the wheel was discovered, some one must have conceived of the idea of dispensing with an assistant by placing a wheel between the poles of the stretcher, thus making a crude wheelbarrow. It is more likely that two wheels were first used, making a cart of the stretcher, because the crude workmen of those days could hardly have produced anything but a very wobbly wheelbarrow. At any rate, the wheel, or pair of wheels, robbed one man of his job. Only one bearer was required where before two had been used. Labor costs were immediately reduced 50 per cent.

DISPLACING MEN WITH MACHINES

In the very earliest days of invention machines began to displace men. Had there been unions in those days, no doubt there would have been strenuous opposition to the introduction of this substitute for an honest worker. But among the ancients, even more than at the present time, invention meant greater production rather than less work, because the laborer of that time was not a hired man but a slave. There was no object in cutting down labor when it cost practically nothing. The only stimulus to invention was greater production.

The invention of the wheel meant the dawn of transportation, which is the backbone of civilization, and from it resulted no end of other inventions. It made it possible for communities to come into closer touch with each other. It meant circulation—an interchange of knowledge and of products. Food was transported from one locality to another, enabling certain communities to dispense with agricultural work and specialize in certain lines of manufacture; for they could barter their products for food raised by other communities. There are some tribes to-day which are most backward because they are separated from other tribes by rivers, while other tribes similarly placed owe their progress to the fact that they have developed sufficient skill to build crude bridges and thus gain access to the outside world.

RAISING WATER

In Egypt the wheel had a wonderful effect on agriculture. In that dry land water is, and always has been, most precious. No wonder the Nile was venerated! It meant life—life to crops, and hence life to man. How to raise water from this stream of life in time of drought was the great problem of the Egyptian. As slave labor was cheap, it was customary to haul up the precious water, a bucket at a time, and pour it over the fields. Then some one discovered that this process could be simplified by using a shadoof or swape; in other words, a long pole fulcrumed near one end, with a heavy rock for a counterbalance lashed to the shorter arm, and a bucket tied by a long rope to the longer arm of the lever. This primitive machine is still to be found in some rural districts. With this contrivance, a heavier load could be lifted than by hand, because, when raising the bucket, the weight of the rock would assist in lifting the water. After the swape came all manner of ingenious devices for lifting the water. There were seesaw arrangements which would scoop up some of the water at each oscillation of the seesaw, and in one ingenious contrivance there was a succession of seesaws by which the water was raised to a considerable height, whence it poured down into ditches that irrigated the fields.

Then some one invented a water wheel or a great wheel, fitted with buckets, which was turned by human or ox power, and which poured a steady stream of water into the irrigating ditches.

But the greatest invention was that of the engineer who actually made the river turn the wheel. It was probably on the Nile that the noria, as this machine was called, was first put into service.

The wheel was provided with paddles, so that the current made it revolve, and the water spilled out of the buckets into a trough as they were turned over by the wheel. We can imagine the triumph of the ancient inventor who developed that machine. True, the river might arise in its wrath now and then and wreck the machine, but in wrecking the wheel it had to flood the land, which, after all, was exactly what was aimed at. The anger of the river was short-lived; it soon quieted down and went on placidly turning the wheel which robbed it of the precious water. It was a great event in the history of engineering. The Nile had been harnessed. One of the great powers of nature had been set to work.

CHAPTER III

MACHINES FOR MAKING MACHINES

WHILE we may glory in the wonderful mechanical progress of to-day, we must not overlook the marvelous skill of the ancient artisan nor forget that it is to his inventive genius that we are indebted for practically every hand tool we possess. Only a few special tools owe their origin to the modern inventor. All the rest date back beyond the twilight of history. We have merely improved upon these tools by slight changes of design or the employment of better materials in their construction.

As users of these tools we cannot begin to compare with the skilled workman of ancient days. Our progress is shown not in the development of skill, but in the loss of it. We have taken the tool out of the human hand and put it into an inanimate machine. It is only very recently that the tool was delivered to the machine and that act marked the dawn of the present remarkable mechanical era.

Machines for making machines date back to the time of the early Egyptians. They had their pole lathes and bow drills, but these machines only partially relieved the workman of his labors, and the quality of the work still depended upon a degree of skill that was acquired only through years of patient apprenticeship.

The pole lathe, by the way, consisted merely of a pair of centers between which the work was mounted, a pole attached to the ceiling and a strap or rope passed around the work and fastened at one end to a pole and at the other to a pedal resting against the floor. (See Figure 24.) When the pedal was depressed, the strap was pulled down and the work was revolved. On releasing the pedal, the spring of the pole pulled the strap up and reversed the rotation of the work. Thus by alternately depressing and releasing the pedal, the work was intermittently revolved against a chisel which was rested on a block and guided by the workman. Small work could be turned out on such a lathe with considerable precision, but when it came to large parts, particularly parts of steel, the workman was easily tired by the effort of operating the pedal and was apt to be irregular in the guiding of the tool.

FIG. 24.—PRIMITIVE POLE LATHE

Up to the middle of the eighteenth century practically no advance had been made over the ancient lathe of the Egyptians, and when, 150 years ago, the steam engine was invented the task of building the engine seemed almost insuperable.

James Watt was a maker of mathematical instruments, a man of great skill and precision as a craftsman, but he dealt with parts of small dimensions. When he conceived of his steam engine, he mentally pictured the various parts as turned out with all the accuracy and finish that was possible in the diminutive members of a scientific instrument. To him it seemed perfectly feasible to turn a cylinder which would be practically perfect in contour, and to fit it with a piston around which no steam could leak. With the lathe then in existence such a fit was easily possible on small work. But when he undertook to have the cylinder of his engine bored, he discovered that there was no machine that could begin to do the work properly. In fact, when Smeaton, who was a prominent engineer of that time, investigated Watt’s steam engine, he declared that it was such a complicated piece of work that neither tools nor workmen existed that could build it. In Watt’s first engine, the cylinder was only six inches in diameter and two feet long, and a special type of boring machine was devised to bore the forged cylinders. But the boring was so irregular that when the piston was inserted and the steam was turned on, nothing would stop the flow of steam that leaked around the piston. In vain did James Watt use cork, oiled rags, tow, paper, and even old hats to stop the leakage. However, the boring machine was improved and later a cylinder, eighteen inches in diameter, was bored with such accuracy that the large diameter exceeded the small diameter in the worst place by only ⅜ of an inch. This Watt considered a very good bit of turning. To-day cylinders of that size that vary from true by half the thickness of the paper that this is printed on would be thrown out as defective.

It was in 1769 that Watt invented the steam engine, but that great event did not mark the dawn of the present era of machinery. For a quarter of a century thereafter there was little progress in the development of machine tools. A boring machine was built that did fair work. There were a few sawmills in which wind power was employed to drive the saw. But lathes were still driven by foot power and the cutting tool was still held and guided by hand.

MAUDSLEY’S “GO-CART”

The real father of the present era was a very clever British mechanical engineer, Henry Maudsley, who undertook to eliminate the uncertainties of the human hand by clamping the cutting tool of the lathe in a rest and arranging the rest to slide along the length of the lathe or transversely toward or away from the center. These two motions made it possible to accomplish all that the workman could accomplish by hand and at the same time the tool was held so firmly that accuracy and precision of turning was assured. Furthermore, he provided this slide rest with a nut that engaged a screw driven through suitable gearing by the lathe spindle. Then, as the work revolved, the slide rest was compelled to move along the bed of the lathe at a uniform rate. By varying the gearing, the speed of the slide rest and the tool it carried could be varied at will, thus making it possible to cut screw threads of any pitch desired with a degree of accuracy unattainable by hand.

Remarkable as was this improvement, it met with the usual opposition that every real advance in machinery received in those days. People referred to the slide rest as Maudsley’s “go-cart,” but it proved such an important element of the lathe and so very valuable that before long it was universally adopted. From that time on the skill of the workman began to lose its importance. The man began to give way to the machine. Precision was possible in large as well as small work. The human element was also dispensed with in the driving of the lathe. The foot pedal was superseded by the steam engine, and the machine came to be known as the engine lathe.

There are many ways of working metals now in common use. Metals may be cast in a molten state, or they may be pressed and molded into shape in a cold state, or they may be hammered either cold or hot, but in nearly all cases in which metal is removed in order to form a piece of work, the chisel is used as a cutting instrument. This is perfectly apparent in lathes and planers, but not quite so apparent in sawing, drilling, filing, and grinding. A drill is merely a spiral chisel which revolves upon its own center. A saw is a gang of tiny chisels, and a file consists of still smaller chisels which are broader than those of the saw. In grinding we have rough surfaces in which particles of emery or carborundum act as tiny chisels. The shears, the punch, and the cutting torch are practically the only exceptions to the rule that metals are always cut by chisels, and even the shears may be conceived as consisting of a pair of broad coacting chisels, while it takes little imagination to see a form of chisel in the punch. The cutting torch is, of course, in no sense a chisel.

In the cutting of metals the work may move against a fixed tool or the tool may move against a fixed piece of work. In a lathe, it is the work that revolves or rotates against the tool. In the drill and the milling machine the tool revolves against the work.