Great Experiments in Physics

Firsthand Accounts from Galileo to Einstein

Morris H. Shamos

• Verlag: Dover Publications
• Jahr: 2012
• ISBN:
  9780486139623
• Thema: Scienze fisiche
• Thema: Fisica

From Galileo's famous experiments in accelerated motion to Einstein's revolutionary theory of relativity, the experiments recorded here trace the evolution of modern physics from its beginnings to the mid-twentieth century. Brought together for the first time in one volume are important source readings on 25 epochal discoveries that changed man's understanding of the physical world. The accounts, written by the physicists who made them, include:
Isaac Newton: The Laws of Motion
Henry Cavendish: The Law of Gravitation
Augustin Fresnel: The Diffraction of Light
Hans Christian Oersted: Elecromagnetism
Heinrich Hertz: Electromagnetic
James Chadwick: The Neutron
Niels Bohr: The Hydrogen Atom,
and 17 more.
Morris H. Shamos, Professor Emeritus of Physics at New York University, has selected and edited the first published accounts of these important experiments and has also added numerous marginal notes that amplify and clarify the original documents. Moreover, the first 19 experiments can be readily re-created by students in a first-year physics course, making the book ideal for classroom and laboratory work as well as individual reference and study.
Finally, Dr. Shamos has provided revealing biographical sketches of the scientists and illuminating references to the political and cultural milieu in which the discoveries are made. The result is a superbly readable presentation — accessible to lay readers — of the crucial theoretical and empirical breakthroughs that altered the course of modern science.

1

Introduction

The Origin of Modern Science

IT IS always inviting, particularly in science, to assign definite causes to each new phenomenon. The temptation is strong, therefore, when seeking the origins of modern science, to set the specific time when it may be said to have started and to determine the sequence of events responsible for it. There was no abrupt starting point, however, and at best we can perceive but a few of the many factors that contributed to the accumulation of this form of man’s intellectual wealth. The history of science cannot be divorced from the political and cultural history of civilization if we seek to account for its development. The arts and the sciences, cultural activities both, tend to flourish in similar social and political environments. The same subtle forces that shape the general cultural atmosphere of a period provide impetus as well to its scientific advancement. This does not mean that periods of vigorous intellectual activity necessarily saw major scientific accomplishment. Far from it! It means only that whenever man felt the urge to engage in cultural pursuits, he contributed—not always constructively, it is true—to the development of science.

Modern science, which is characterized by rational thought and by methods that have led successfully to an understanding of natural phenomena, is relatively recent, having its origin in the seventeenth century. But its roots may be traced, by a sometimes tortuous path, to ancient Greek culture. It is important to distinguish between the orderly structure we know as science and the empirical; technological development resulting from man’s efforts to control his environment. The latter, sometimes called “practical” or “applied” science and involving for the most part trial-and-error methods, dates back virtually to the dawn of civilization. However much these discoveries—for example, in metallurgy, ceramics, irrigation, and the mechanical arts—may have contributed to the growth of civilization, the methods—and motives—that led to them must not be confused with the planned experimentation by which we seek to confirm our modern views of nature.

It would be a mistake to conclude that only in the last three hundred years has man been concerned with the search for truth. Earlier civilizations were no less interested in knowledge nor less curious about the nature of things. The essential difference lies in the fact that the earlier methods by which such knowledge was sought were not adequate to reveal the truth about the physical universe.

The Golden Age of Greece, the fifth and fourth centuries B.C., saw the beginnings of a system of natural philosophy that was to dominate man’s scientific thinking for centuries to come. This was the period of the famous teacher-pupil sequence: Socrates, Plato, and Aristotle, probably three of the most remarkable individuals in the history of thought. All believed in the existence of universal or absolute truths, which man could discover if he would simply pursue the proper methods. They looked upon knowledge not as a means to utilitarian ends but as a means to satisfy human curiosity. And they held that true knowledge, as distinguished from knowledge derived via the senses, could be deduced by purely formal methods, i.e., by a system of logic. The use of some forms of logic apparently dates back to the pre-Socratic period of the sixth and fifth centuries B.C., when philosophers first showed concern over the internal consistency of their arguments. But it was Socrates and Plato who put deductive logic to such skillful use and Aristotle who invented the logical device known as the syllogism.

The Socratic method of reasoning found ready acceptance among the knowledge-loving Greeks, who became masters of deduction—and the victims of its weaknesses. Deduction is the process by which one proceeds to the solution of particular problems through the application of general principles. It involves drawing logical or valid conclusions from given premises, by assuming the ultimate truth of these premises. If we assert, for example, that x is greater than y, and y greater than z, we conclude that x is greater than z. The conclusion is a necessary consequence of the premises, and while the deduction is clearly correct the truth of the conclusion rests upon the reliability of the initial statements. It should be evident, then, that deductive reasoning does not necessarily lead to new knowledge, for it provides no recipe for testing the truth of the basic assertions.

The syllogism represents a particular form of deductive argument, having a structure frequently found in ordinary discourse. It consists of a general premise, assumed to be true, followed by a statement which makes use of the general premise in a specific case, and finally a logical conclusion. As an example, we might use the syllogism to derive a typical Aristotelianlike explanation for the acceleration of falling bodies:

The traveler hastens when approaching his destination.
A falling object may be likened to a traveler. . . .
Hence, falling objects accelerate as they approach the earth.

The argument is obviously defective in its premises. Even granting the (questionable) validity of the first premise, the analogy drawn in the second has no basis in fact. Yet the conclusion follows logically from these statements and illustrates how the followers of Aristotle employed his deductive system to “account” for natural phenomena. Such reasoning from false premises to a correct conclusion is unfortunately all too common, even today, in the area of explanation. The conclusion is correct, of course, because it stems from observation and the premises designed accordingly, not because it follows from true statements.

The example given represents but one of many variations of the syllogistic form of argument. It is actually more an example of dialectic than of scientific argument. In the final analysis the latter reasons from true premises while the former only from “probable,” or even “plausible,” statements. The formal logical methods by which such reasoning may be examined for self-consistency were already developed to a high degree by the start of the Hellenistic period (with the death in 323 B.C. of Alexander the Great, who had been tutored by Aristotle), during which they formed the foundation for the remarkable mathematical proofs of Euclid (c. 323–c. 285 B.C.) and Archimedes (287?–212 B.C.). However appropriate the deductive method may be in many branches of mathematics, it cannot serve alone as the means for understanding nature. The essence of physics, indeed of any natural science, is to account for nature in the simplest possible terms; that is, to reduce all that we observe to basic principles, or causes. This is what we mean by an explanation in science and is the way we discover new scientific knowledge. It is this economy of thought and of expression that characterizes explanation in modern physical science. But how do we find the basic causes of things? How do we establish the truths of our initial premises when arguing deductively? It is here that the Aristotelian procedure fails and we must seek other methods.

Aristotle differed from Plato and Socrates in part by his marked interest in natural phenomena and his higher regard for practical matters. He was not adverse to experimentation, although he could hardly be considered a thorough experimenter. Sometimes called the encyclopedist of ancient science because of his careful systematic observations in descriptive natural history, on which rest his chief qualifications as a “scientist,” Aristotle nevertheless held the most naive and confused views regarding the nature of the physical world. Much as he contributed to the development of biology, it is because of his inferior physical reasoning that one finds so regrettable his great influence over succeeding centuries of scientific thought. There can be little doubt that it was largely his authority that served to delay so long the full evolution of such areas as dynamics, atomism, and astronomy. Some two thousand years later we are to find the founders of modern physics, such as Gilbert, Galileo, Boyle, and Newton, having to reject the prevailing doctrines of Aristotle before setting science on a firm foundation.

There are a number of probable causes for Aristotle’s unsound doctrines in physical science. First of all, he failed to make effective use of the process of induction. This is the inverse of the deductive method and consists essentially in proceeding from the particular to the general; that is, in reasoning from a limited number of observations to a general conclusion that embraces all similar events. It is by this method that we establish the initial truths, from which we can then proceed, by deduction, to account for our particular experiences, and thus to test the reliability of the induction. Aristotle was familiar with the inductive method; in fact, he was the first to outline its principles. Perhaps he distrusted it as a means of gaining knowledge, or perhaps he failed to recognize its place in scientific reasoning. At any rate he did not make use of this highly significant form of argument. Instead, the generalizations that were to form the initial premises in his deductive arguments were derived either by pure intuition or by appealing to the ends or purposes (generally human) they served, that is, by teleological argument. This is not to say that intuition has no place in inductive reasoning; but it is intuition born of experience rather than the introspective inventions of Aristotle that distinguishes the modern use of induction.

All of our physical theories are generalizations from experience. When Newton declared that “Every body perseveres in its state of rest, or of uniform motion in a straight line . . . , ” he clearly had proceeded by induction from a limited number of observations to a sweeping generalization that applies to the entire universe. How valid is such a procedure? By its nature it cannot yield absolute certainty. Its reliability, then, must be measured by its success in meeting the challenge of continued scientific testing. Each new observation that agrees with the conclusions implied by a hypothesis reached through induction adds both to the strength of the hypothesis and to the power of the inductive method generally.

Aristotle’s physical arguments were largely nonmathematical; they were qualitative rather than quantitative and lacked the abstraction that is the power of modern physics. Nor did he resort to critical experiment to test the conclusions deducible from his premises. Leonardo da Vinci (1452–1519), the remarkable Florentine painter who was among the first to hammer at the crumbling walls of medieval science, held that true science began with observation; if mathematical reasoning were applied, greater certainty might be reached, but “those sciences are vain and full of errors which are not born from experiment, the mother of all certainty, and which do not end with one clear experiment.”¹

Consider, for example, Aristotle’s views on the nature of matter, about which there had been considerable speculation even in pre-Socratic Greece. Is matter continuous and divisible indefinitely, or is it made up of basic units beyond which it cannot be further divided? This question had puzzled curious men for ages and was not finally resolved until the last century. An atomistic view of nature, which postulated a huge number of invisible particles in a sea of empty space, was invented by Leucippos about the middle of the fifth century B.C. and developed more fully some thirty years later by Democritus. “According to convention,” said Democritus, “there is a sweet and a bitter, a hot and a cold, and there is color. In truth, there are atoms and there is a void.” Certainly this was an oversimplification of nature, and a scheme based purely on philosophical speculation that could not be subject to test—but one which, in form, bears some resemblance to the modern atomic viewpoint.

At the other extreme were the continuists, among them Anaxagoras, the famous Athenian teacher of the fifth century B.C., and later, Aristotle. According to this school of thought all matter was composed of the same primordial stuff called hyle, and the differences among substances resulted from the presence in them of various amounts of certain properties given the hyle by four basic elements: fire, earth, air, and water. It was Aristotle’s notion that these elements tend to arrange themselves in concentric fashion about the center of the world, with the earth at the center surrounded by successive shells of water, air, and fire. Coupled with this was the doctrine of natural places: Everything was assumed to have its “proper place” in nature, that of heavy things was below and that of light things, above. This “accounted” for the descent of stones, for example, and the fact that air and fire tend to rise.

Space will not permit a thorough discussion of Aristotle’s scientific doctrines. His astronomical speculations and his views on motion were no less obscure than his conception of matter. It is perhaps inevitable that the science practiced by Aristotle should invite little more than ridicule from students of modern physics. One should bear in mind, however, that the Greeks generally did not have the experimental tradition in science that we now consider so essential, and that Aristotle’s views would appeal to many of his contemporaries simply because of its speculative and seemingly rational nature, and their agreement with what appeared to be “common sense.”

It should not be concluded that all Greek physics was as barren as Aristotle’s; on the contrary, there were occasional flashes of brilliance throughout ancient Greece. We have mentioned the mathematical accomplishments of Euclid and Archimedes. The latter solved physical problems in a completely modern fashion; he made full use of the mathematical tools available to him, and he exhibited a remarkable degree of abstraction for his period. His treatment of hydrostatic problems (Archimedes’ principle) stands out as the most significant accomplishment in physics prior to the scientific revolution. In applied science Hero of Alexandria, who lived in the last century B.C., was responsible for an impressive array of practical inventions. By comparison with the Middle Ages, Greek science was truly prodigious. -

Science in the Middle Ages

We have said nothing of Latin physics during the Hellenistic period for the reason that, while her engineering achievements were substantial, Rome had virtually no independent science. Instead, under the influence of Greek civilization the Romans became students of Greek science and were content to follow its dictates—even while constructing great systems of aqueducts, sewers, roads, harbors, and public buildings. They were too much concerned with practical problems to make original contributions in science. Of particular significance to scientists of the early modern period (sixteenth and seventeenth centuries) was a didactic piece written by the Roman poet Lucretius in 57 B.C. Entitled Of the Nature of Things (De Rerum Natura),² it popularized the atomistic view of matter in the most eloquent and lyrical fashion. While not a work of science, it was to have considerable impact centuries later upon scientists seeking to overthrow the prevailing Aristotelian doctrine of the four elements.

Throughout the period of the Roman Empire³ and the Middle Ages that followed, physical science virtually stood still. Greek science was lost from view in the first few centuries of the Christian era; it was replaced largely by superstition and mysticism. Rational thought gave way to divine revelation as the test for truth, and the authority of the Scriptures dominated all philosophy. Interest in natural phenomena was replaced by an ethical and moral philosophy that reflected man’s primary concern with religion. In such an atmosphere intellectual activity could hardly exist, let alone prosper.

An important pseudoscientific product of the early Christian era was the practice of alchemy, which included the art of transmuting base metals into precious metals such as gold and silver. It was Aristotle’s view of matter, his use of the “four elements,” that provided the theoretical basis. If substances differed only in their relative proportions of the four elements, it followed that by appropriate changes in these amounts matter could be altered at will. Alchemy had its origin in Alexandria;...

Inhaltsverzeichnis

• DOVER BOOKS ON PHYSICS
• Title Page
• Dedication
• Copyright Page
• Preface
• Table of Contents
• 1 - Introduction
• 2 - Accelerated Motion
• 3 - Boyle’s Law: Pressure-volume Relations in a Gas
• 4 - The Laws of Motion
• 5 - The Laws of Electric and Magnetic Force
• 6 - The Law of Gravitation
• 7 - The Interference oƒ Light
• 8 - The Diffraction of Light
• 9 - Electromagnetism
• 10 - Electromagnetic Induction and Laws of Electrolysis
• 11 - Lenz’s Law
• 12 - The Mechanical Equivalent of Heat
• 13 - Electromagnetic Waves
• 14 - X-Rays
• 15 - Natural Radioactivity
• 16 - The Electron
• 17 - The Photoelectric Effect
• 18 - The Elementary Electric Charge
• 19 - Induced Transmutation
• 20 - The Neutron
• APPENDIX 1 - The Electromagnetic Field
• APPENDIX 2 - The Quantum Hypothesis
• APPENDIX 3 - The Theory of Relativity
• APPENDIX 4 - The Hydrogen Atom
• APPENDIX 5 - The Compton Effect
• Index
• DOVER SCIENCE BOOKS