The realities of modern science, an introduction for the general reader

Front matter

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BOUGHT WITH THE INCOME OF THE

Preface

The present volume is intended for the general reader, interested in modern science, who finds few clews to recent advances in his memories of the formal instruction of school or college days.

During the last twenty years physical research has penetrated the mysteries of the chemical elements and has demonstrated that their atoms are granular in structure and electrical in nature. Transmutation — the dream of the alchemists — is to-day recognized as a natural process in the case of radioactive substances. An element common to all matter has been found in the electron which has been isolated and studied. It is a reahty of modern science and in terms of it scientists are rapidly explaining the phenomena of all physical science, the essential unity of which its discovery has emphasized.

The existence of electrons and their determining effect in the composition of the chemical elements are easily demonstrable facts, compared to which the indestructibility of matter is a speculative assertion and the independence of mass and speed an exploded theory. Nevertheless our education is so constrained by established curricula and text-books adapted thereto, that a knowledge of these facts is usually acquired only by college students who elect the more advanced courses. Even in the subject of electricity most of

Vlll PREFACE

the phenomena are treated in elementary courses without reference to the electron, the fundamental entity.

One difficulty seems to be that physical science is subdivided, classified, and named until the unity is completely obscured. Of each subdivision the accepted method of instruction assigns certain phenomena to high school or sophomore courses and others to junior work. The results of recent researches are postponed for consideration in graduate courses and "recent" often means since the graduation of the instructor. The selection of material for elementary courses is not always determined by whether or not the phenomena are fundamental and easilv comprehensible, for it is largely traditional. For example, the writer remembers discussing a well-known text-book with a high school teacher, who said it was not adapted to his field because it introduced the "Brownian movement." The writer, however, believes that the Brownian movement is capable of simple presentation (cf. pp. 155 and 158) and should be discussed in order that the student may obtain satisfactory concepts upon which to base his future study.

So far as concerns college instruction one alternative is a general introductory course which cuts across the conventional divisions of subject matter, selecting to emphasize the unity. Nor should this introduction have the finality of the usual elementary course, for it should indicate the evolutionary character of science and lead up to present problems. It should also indicate the historical aspects and the social significance of modern science. In material it should be adapted

PREFACE IX

to the future citizen rather than the future scientist, to general readers rather than technical students. The present book follows one of the many possible outlines for such an introduction and constitutes a suggestion as to one of the changes in teaching methods which our educational system seems to require.

The general reader is under no compulsion from a traditional curriculum and may pick and choose his sources of information. To the study of science he may, however, need an introduction and this need the present volume attempts to satisfy. The earlier chapters following an historical order develop without abstract formulations the fundamental concepts of modern science. By the |ime Chapter IX is reached the necessity of algebraic expression has become apparent and the three succeeding chapters illustrate its usefulness while developing the ideas of defining equations, rates, and the laws of motion. Not all these ideas are symbolized and the reader who feels an ineptitude for mathematical expressions is advised to give these chapters a cursory and mechanical reading in order to reach the important chapters on molecular and electronic motions.

The majority of readers will probably find no obstacles in the occasional formulas of the later text. For these the book may serve as an introduction to the general literature of physical science. To this end footnotes refer to books on special subjects, the greater portions of each of which the reader will find comprehensible in case he is interested in more detailed study.

The writer wishes to make an acknowledgment to the Physics Department of Mount Holyoke College,

X PREFACE

Professor Laird, the head of the Department, and Dr. Shields read this book in manuscript during the summer of 1918. Miss Shields has followed the general method and incorporated some of the material in a course for second year students. For this proximate use of the manuscript and for the suggestions which have arisen from it the writer expresses his thanks to Miss Shields. Thanks are also expressed to Dr. K. K. Darrow of the Western Electric Company, who has read the proof.

J. M.

Research Laboratories The Western Electric Company, Inc.

March 1, 1919

Contents

CHAPTER PAGE

Preface vii

I The Beginnings of Knowledge .... 1

Chapter I

Man is sometimes distinguished as a "tool using" animal. Monkeys may be taught a few simple operations with tools, such as cracking nuts with a stone, but usually they merely mimic a man. Their hands, with five fingers instead of four and a thimib, are not suitable for picking up objects. Other animals have bodies the parts of which are convenient for various purposes, as horns for defense or claws for offense, but parts of the body, even though they serve a special purpose, are not tools. A tool is an object apart from its user.

Man's superiority as a tool user, partly physical in his ability to stand erect and use his hands, and partly mental, ultimately secured his position over the beasts of the world and enabled him to construct our material civilization. An instance of the mental difference is found in the attitude toward fire. The dog knows the pleasure on a cold day of curling up beside the fire. For thousands of years he has been man's companion and intelligent servant. Nevertheless, a dog, shivering before a dying fire, lacks the ability to foresee effects,

B 1 which would lead him to push a new stick into the smoldering embers.

No one knows how man first learned to keep fire alive and how ages later he learned to make a fire. Many students of the relics of man in earlier geologic ages think that he first saw fire in the dry seasons when lightning had started it. Perhaps after a brush fire had been checked by a rain, some man, more adventurous and curious than his fellows, approached and picked up a burning stick. The man who was the first in the world to pick up a brand. was not only brave but an important discoverer, in showing that fire could be safely handled. Nobody told him that although wood is combustible and if heated to the proper temperature will ignite with air and burn, still, when below this temperature, it is a very good heat insulator. The experimental fact preceded by ages its scientific description.

Probably other members of this discoverer's family imitated him, just as small boys around their first bonfire will soon follow the lead of the older boy who brandishes a flaming stick. From this time familiarity with fire increased, although the first fire-handlers may have died before they again saw fire, leaving the discovery to be remade by a later generation.

Perhaps, chilled by the rain which checked the spreading bush fire, our man may have discovered the pleasantness of warming his own body beside the embers. He may also have tasted roasted meat for the first time, driven by hunger to try the half burned body of some small animal which was caught in the fire. If so, it was a long time before he ate cooked meat again, for fires could only start in the dry season from lightning or from a volcanic eruption.

In the next dry season our man may have remembered his first taste of cooked meat. More probably he did not remember at all. Certainly his brain did not permit of his looking ahead and sajdng, "Next dry season, if there is a fire, I may find some roasted meat." His mind developed slowly, and the first experiment had to be performed many times by different members of the race before he was ready for his second step in the domestication of fire. History^ incompletely depicts these slow ages, the dark nights, the cold and rainy days, and the uncooked food.

How man learned to keep a fire alive is also a matter of surmise. Perhaps he noted that it lasted longest in large heaps of damp brush or in the trunks of rotten trees. At some such remains of a fire given by lightning from the heavens he may have cooked meats and noticed that the fire flared up under the breeze. Another discoverer may have carried home to his cave a glowing brand, which when thrown aside into the dry branches started a larger fire. By such a series of accidents the discovery may have been made that fire could be kept by furnishing it with fuel, and that it burned less fiercely and lasted longer if covered from the wind.

As yet no way was known of kindling a fire. If the fire died, the tribe had to beg or steal from another tribe or wait until a dry season when nature again provided fire. To-day we httle realize the situation of

• An interesting sketch of this evolution is that of Migeod, "Eaxliest Man," Kegan Paul, London, 1916.

mankind when its scientific knowledge was only sufficient to maintain a fire and not to start one. It is no wonder that religious rites grew up about the tribal fire and that special^ caretakers were dedicated to it.

While early man was learning some of the uses of fire and how to conserve and control it, he was also developing tools and through their use making advances in clothing and shelter. His first tool might have been a stone. Perhaps, while lying on the floor of his cave, he was frightened by the entrance of a wild beast and his hand closed over one of the small stones which he had earlier brushed aside to make a smoother bed. He fought blindly and the stone slipped from his grasp. A chance hit, the astonished beast turned tail, and he was saved.

The next time he was attacked he may have remembered the episode of the cave and used a stone again. If his brain was not sufficiently developed for him to connect the act with the flight of the beast he was probably eaten for his ignorance. Those families or tribes which quickest learned this use of stones were fittest to survive.

A peaceful use of stones as agricultural tools may or may not have preceded their use as weapons. Early man, we believe, dug for roots and in certain seasons these were the only succulent food which he could obtain. While burrowing with his hands he might strike a stone and instinctively grasping it continue the same digging motion. If the stone happened to be the right shape he found to his surprise that his work went faster and easier. Later he may have tried it again and found by bitter experience that round smooth stones retarded his operations. Still later some man may have broken a stone by throwing it against a rock, hoping to find among the pieces one suited to his needs.

In some such way there developed the idea of using tools and of forming them. Of course, it is only a small step from breaking the stone as just described and chipping off edges of the selected stone so as to form it more nearly to the desired shape. But this step may not have been taken for centuries. Even if some man did make this advance and his tribe learned it from him, accident or disease could have destroyed them all and with them the precious knowledge. There were as yet no records of past achievements to save a student the mistakes and trials through which ages of mankind accumulated and arranged its knowledge of the physical world.

If food became scarce in the region where lived a tribal group which had learned to preserve fire it may have wandered into other regions and so spread its special knowledge. This change from the old conditions and the necessity of meeting new ones would have stimulated it to new discoveries along other lines, as perhaps in the making of vessels for carrying fire and water on its travels. In this migration it may have met another tribe with other knowledge. If they fought the weaker tribe perished with its knowledge, or if they mingled the enlarged group enjoyed the knowledge common to its parts.

Except when tribes amalgamated the exchange of information must have been very slow because of the difficulties of language. At this time in the development of man he was just learning to talk. His few ideas and fewer words were concerned with concrete objects such as water, fire, food, sun, and moon or with his own sensations such as cold, hunger, and fatigue. He had no vocabulary for expressing abstract ideas. Imagine the difficulty of trying to tell a primitive man of the speed record of an automobile, of the efficiency of its engine, or of the refinement of its lines and upholstery.

Between the discovery of the method of conserving fire and its production by a simple machine many thousands of years must have intervened. A primitive method is that of rubbing a sharp stick back and forth in a groove cut in a block of hard wood. For this concrete case he had learned that his work in rubbing together two surfaces resulted in heat. The heat produced by his efforts did not diffuse rapidly and so make the entire block of wood a little warmer than it was before. Instead it was concentrated in the wood adjacent to the groove. If he rubbed hard enough, that is, if he did enough work, this part of the block would then rise rapidly in temperature, smoke, and finally set fire to dry wood dust or other tinder placed in the groove. '^

This simple device is not, however, a machine. It is merely a special tool for rubbing and a block to be rubbed. When primitive men arranged a combination where the rubbing tool was actuated by another part of the device, which part in turn was controlled by the operator, then he had a machine. In Fig. 1 is shown such a fire-making machine. It is of course a develop-

Fig. 1.

ment of an earlier form, shown in Fig. 2, where a pointed

stick or drill is twisted by the operator's hands. Let us examine this

primitive machine more

closely. The operator,

forcing the bow back and

forth, causes its various

points to move along

parallel paths. There is

no turning of the bow,

so its motion is "translation." The machine

then converts a motion

of translation into one of

rotation. The cord of

the bow merely replaces

the hands of the operator. In turning the drill of

Fig. 2 through one complete revolution each hand

comes in contact with every point of its circumference and moves a distance equal to the circumference. When the drill is operated by the bow, the latter must move through an equal distance. The operator may use only one hand with the bow, but, obviously, he must push or pull twice as hard since his other hand is not assisting. The advantage

of the machine is not that it requires less work, but

that it is more convenient, requiring only the simple

Fig. 2.

motion of pushing and pulling. To operate the hand drill requires skill and practice, but to operate the machine requires less skill and the ability to work.

From this primitive design we can obtain a concept of a machine as a device in which a motion communicated to one part results in a different motion of a second part. Now, although this is a correct statement, it is one that is lacking in human interest or significance. Early man devised machines in his struggle against the rigors of the world about him. From our standpoint, as well as from his, we should consider the machine with reference to its effect on mankind.

It is work to draw the bow back and forth against the friction of the drill and the block. We call the abihty to do work "energy" and say that when work is done energy is expended. The machine requires energy from some source, and material upon which to operate. Push and pull, push and pull, is all that it requires, for in its sequence of motions it accomplishes the results of the most skilled craftsman. And this sequence of events is determined once and for all by the inventor of the machine. The needle of the sewing machine rises and falls on the material beneath it whether it be cloth or the hand of the operator. The loaded gun shoots friend and foe alike provided only the energy in its cartridge is released.

A machine, then, is a device for producing a definite sequence of motions provided the supply of energy necessary to operate it is released. Unless the machine is broken, in which case, of course, it is not a machine at all, man's only control of it is a permissive one, of allowing it to run or not, by controlling its supply of energy. In our modern life where machines for varied purposes are available this control is obtained by means of a switch or button, a faucet or a throttle. It is ours to say whether or not we shall release the energy, but otherwise the operation is inherent in the design of the machine except in so far as a counteracting machine, like a brake, may be available. In such a case, this too is controlled by its switch, throttle, or lever.

A machine, once started and supplied with energy, performs its characteristic series of operations without reference to their effects. In the inevitability of the sequence for which the machine is designed inhere its advantages and dangers. It is therefore vitally necessary that those who control machines or come within the range of their motions should bear in mind this fact. For this reason the old adage of "Look before you leap " has been replaced by the modern slogan of " Safety first."

The machine requires a source of energy, but does not demand an intelhgence or skill on the part of the operator proportional to the results which it produces. While this permits the unskilled to produce the results of the skilled it does not offer the changing conditions which stimulate mental growth. There is a sameness to its operations which may make the human agents mere appendages of the machines they seem to control. The social and economic significance of the machine industry is only beginning to receive from economists and educators the consideration it deserves. Laws on manufacturing conditions and on child labor indicate a growing appreciation on the part of the public and its statesmen of a few of the problems involved.

With the control over fire, and the consequent abihty to cook food and to maintain a comfortable living temperature, man's ascent toward civilization really began. During this time he devised and employed many simple machines, some of which we shall describe in a later chapter. From living in crude shelters of boughs and leaves or in caves he came to live in tents and houses. From being dependent on wild fruits and meats he advanced to agriculture. Animals of burden were used as machines with internal sources of energy. Boats were made and fitted with oars, which are of course simple machines, and also with sails by means of which the energy of the wind could be utilized. Larger groups of men could now exist in the same region, and cities and villages were formed. With the lessening of the struggle for existence man obtained more time for thought and mental development. The large empires of the ancient world and their civilizations were founded on these elementary advances in the knowledge of the physical world. Language and the arts had developed so that with two of these empires, Babylon and Egypt, history as we know it really began. With these there also began that arrangement and correlation of knowledge which we call science.

Both the Babylonians and the Egyptians were agricultural peoples, one living in the fertile valley of the Euphrates, the other on the banks of the Nile. What scientific advances they made were mostly along lines of immediate practical value. Thus, the Egyptians are believed to have learned mensuration and started the science of "earth measurements," or geometry, because of the necessity of marking anew each year the boundaries of fields flooded by the Nile. They did not carry their development, however, beyond the simple ideas necessary to lay off plots of ground and to compute areas and volumes. It was left for the Greeks to develop later the abstract ideas and general methods of reasoning which we know to-day as geometry.

Both these peoples were highly religious. With their lack of scientific knowledge it was but natural that they should be superstitious about the stars, and that their knowledge of astronomy should develop in connection with their rehgion. To the Babylonians we apparently owe the grouping of days into longer periods called weeks. Why seven days were chosen for the latter period is evident from our names for these days, which are traced in derivation to the sun, the moon, and the five planets, Jupiter, Mercury, Mars, Venus and Saturn.' The lunar month was of course early noticed and measured by these astronomers. They had also progressed far enough to measure the year as 3651 days and to determine other astronomical facts.

These facts were developed in connection with their rehgion and their practical needs. In Babylonia, where stone was not easily obtainable and brick was used for building, one of the months was named for the brickbuilders. In this month, apparently, the

1 Cf. Libby, "An Introduction to the History of Science," Houghton Mifflin Company, 1917.

clay and the atmosphere best suited this work. In Egypt, on the other hand, great interest was taken in the various constellations in which the sun appeared at dawn. The heliacal rising of Sirius marked the annual inundation of the lands adjacent to the Nile and began the calendar year.

It is interesting to note, also, that the division of hours and minutes, each into sixty parts, may be traced to the Babylonians. Although they had a decimal system of numbers, they also had a sexagesimal system. In their system of weights, starting with a "shekel" equivalent to about half an ounce, they had a unit, the "mina," sixty times as large, and also a unit, the " talent, " which was equal to sixty minas.

In general, both these early races were singularly lacking in curiosity as to the world in which they lived, as to its natural laws, its origin, and its composition. They did, however, invent new contrivances and thus showed a practical familiarity with some of the phenomena of nature. As early as 4000 B.C. the Egyptians had learned to melt iron oy using a bellows to make the fire burn hot enough.

In some respects their temperament was like our own. They were interested in practical applications and were unconcerned or even impatient of attempts to classify and coordinate their knowledge and to speculate upon the fundamental causes of the phenomena which they observed. They did not realize that practical devices follow and do not in general precede advances in scientific knowledge. In the case of the Egyptians this lack of speculative interest was combined with a feeling that in their religion they had reached a finality. As a result there was a long period in which they made small progress and during which they were passed by other races.

The rise of one of these, the Greek, is marked in its early stages by contributions from the Semitic race, of which the Babylonians and Egyptians were both members. The Island of Crete first received the culture of the Semites from the Egyptian, Assyrian, and Phoenician sailors and merchants. But the Greeks also were intrepid sailors and shrewd merchants, and they were shortly to be found in the older centers of learning. With one of these Greeks, an Ionian of Phoenician descent, Thales of the Island of Miletus, science as well as Greek philosophy is considered to have begun. This was about 585 b.c.

Chapter II The Riachines Of The Ancient World

In the homes of the earlier civilizations are buildings and monuments which have withstood the ravages of time and the waves of hostile invasion. Often these records of man's earUer activities are only restored to sight by excavation, for they have been covered by the dust of succeeding ages. The temples and palaces, the city walls, and the monuments of Egypt and Asia were of stone or brick, but the houses of the common people were usually of mud. When a conqueror razed a city, holes were broken in the walls to render it less easily defended ; the monuments of the kings and the altars of the local gods were toppled over ; and the houses of the common people were reduced to dust. The large buildings, of course, took years to restore, and the weakened and terrorized inhabitants may have hesitated to rebuild what had so recently been destroyed by their enemy. Thus in time the traces of a city were lost beneath the mud and rubbish of succeeding generations.

Such relics as we have, suggest to the engineer of to-day the question : How did the ancients, with their limited knowledge of physical science, succeed in erecting such enormous and high structures? The answer is to be seen partly in their knowledge of certain simple machines and partly in their organization of society. They were familiar, we know, with some or all of six mechanical contrivances, known as the six simple machines. These are the lever, the inclined plane, the wedge, the puUey, the screw, and the wheel and axle, conventionally illustrated in Fig. 3. Let us see what the advantages of these devices would be.

The lever consists of a bar. If the distance from the fulcrum, c, to the point a, where the force is applied,

Fig. 3, is larger than that to the point b, then, as we know, the lever gives a mechanical advantage. The force exerted at b by the lever is as many times greater than the force appUed at a as the distance ac is greater than be. It was not until the time of Archimedes (died 212 B.C.) that men knew this rule. During preceding centuries, however, they must have had a very good working knowledge of the lever.

When a man wanted to raise the end of a block of stone he probably selected a bar which looked about long enough and tried. If it didn't work he pushed the fulcrum a little closer to the block and tried again. If the force he was capable of applying was still too small, he tried a longer lever. He thus made the lever arm of his force sufficiently greater than that of the weight he was trying to lift. Of course, if he chose too long a bar it may have bent in such a way as really to make his lever arm shorter. In some such manner the ancients probably obtained their knowledge of the lever and incidentally some ideas as to the bending and elasticity of beams.

We know to-day another property of the lever of which they made use, although it was not formally and completely described in words for centuries. We recognize that the motion of a lever is a rotation about its fulcrum, the path which any point travels being a part of a circle about the fulcrum. Obviously, in any motion, the more distant points must move through the greater distances. But the time it takes each point to move through the arc of its circle is the same. Hence the point that moves the farther must also move the faster. This is the property which we use whenever we want to strike faster than we can with the levers afforded us in the bones of our bodies, as in using an ax, a sword, or a golf club. The system of levers involved in an ordinary typewriter is an interesting illustration of a slow motion of the point where the force is applied producmg a faster motion of another point of the system.

In the case of the lever, as of all machines, work is done by the machine only because work is done on it.

Now, we know that when we push or pull, the work we do depends not only upon how hard but upon how far. When one pushes on the long arm of a lever and lifts a larger weight at the end of the short arm, he must push a correspondingly greater distance than the weight rises.

The inclined plane is strictly speaking not a machine. Its serviceability was probably evident to man fairly early in his development. He would have noticed ' that he could drag a burden up the smooth inclined face of a rock more easily than lift it through the same vertical distance. In his building operations he learned something of what builders to-day call the "angle of repose" of a loose material. When we try to make a pile of sand or gravel we notice that if the sides become too steep, what we put on slips down. If we do not exceed a certain steepness, that is, a certain angle of repose, then the friction which the surface offers prevents what we add to the pile from sliding down. The steeper the inclined plane, the more easily do things slide down and the greater the difficulty of dragging them up. For this reason the slope of the incUne should be gradual. It is also desirable to reduce as much as possible the friction between the body and the surface of the incline. Of course, on roads this is usually accomplished by making the friction between the two surfaces rolling rather than sliding friction. With these ideas the ancients were familiar.