Popular Scientific Lectures

Part 1

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POPULAR SCIENTIFIC LECTURES.

BY THE SAME AUTHOR.

THE SCIENCE OF MECHANICS. Translated from the Second German Edition by T. J. McCormack. 250 Cuts and Illustrations. 534 Pages. Half Morocco, Gilt Top. Price, $2.50.

CONTRIBUTIONS TO THE ANALYSIS OF THE SENSATIONS. Translated by C. M. Williams. With Notes and New Additions by the Author. 200 Pages. 36 Cuts. Price, $1.00.

POPULAR SCIENTIFIC LECTURES. Translated by T. J. McCormack. Third Revised and Enlarged Edition. 411 Pages. 59 Cuts. Cloth, $1.50; Paper, 50 cents.

THE OPEN COURT PUBLISHING CO., 324 DEARBORN ST., CHICAGO.

POPULAR SCIENTIFIC LECTURES

BY ERNST MACH

FORMERLY PROFESSOR OF PHYSICS IN THE UNIVERSITY OF PRAGUE, NOW PROFESSOR OF THE HISTORY AND THEORY OF INDUCTIVE SCIENCE IN THE UNIVERSITY OF VIENNA

TRANSLATED BY THOMAS J. McCORMACK

THIRD EDITION, REVISED AND ENLARGED

WITH FIFTY-NINE CUTS AND DIAGRAMS

CHICAGO THE OPEN COURT PUBLISHING COMPANY

FOR SALE BY

KEGAN PAUL, TRENCH, TRUEBNER & CO., LONDON

1898

COPYRIGHT

BY THE OPEN COURT PUBLISHING CO.

Pages 1-258 } } in 1894. Pages 338-374 } Pages 259-281 in 1896. Pages 282-308 in 1897. Pages 309-337 in 1898.

AUTHOR'S PREFACE TO THE FIRST EDITION.

Popular lectures, owing to the knowledge they presuppose, and the time they occupy, can afford only a modicum of instruction. They must select for this purpose easy subjects, and restrict themselves to the exposition of the simplest and the most essential points. Nevertheless, by an appropriate choice of the matter, the charm and the poetry of research can be conveyed by them. It is only necessary to set forth the attractive and the alluring features of a problem, and to show what broad domains of fact can be illuminated by the light radiating from the solution of a single and ofttimes unobtrusive point.

Furthermore, such lectures can exercise a favorable influence by showing the substantial sameness of scientific and every-day thought. The public, in this way, loses its shyness towards scientific questions, and acquires an interest in scientific work which is a great help to the inquirer. The latter, in his turn, is brought to understand that his work is a small part only of the universal process of life, and that the results of his labors must redound to the benefit not only of himself and a few of his associates, but to that of the collective whole.

I sincerely hope that these lectures, in the present excellent translation, will be productive of good in the direction indicated.

E. MACH.

PRAGUE, December, 1894.

TRANSLATOR'S NOTE TO THE THIRD EDITION.

The present third edition of this work has been enlarged by the addition of a new lecture, "On Some Phenomena Attending the Flight of Projectiles." The additions to the second consisted of the following four lectures and articles: Professor Mach's Vienna Inaugural Lecture, "The Part Played by Accident in Invention and Discovery," the lecture on "Sensations of Orientation," recently delivered and summing up the results of an important psychological investigation, and two historical articles (see Appendix) on Acoustics and Sight.

Part 2

The lectures extend over a long period, from 1864 to 1898, and differ greatly in style, contents, and purpose. They were first published in collected form in English; afterwards two German editions were called for.

As the dates of the first five lectures are not given in the footnotes they are here appended. The first lecture, "On the Forms of Liquids," was delivered in 1868 and published with that "On Symmetry" in 1872 (Prague). The second and third lectures, on acoustics, were first published in 1865 (Graz); the fourth and fifth, on optics, in 1867 (Graz). They belong to the earliest period of Professor Mach's scientific activity, and with the lectures on electrostatics and education will more than realise the hope expressed in the author's Preface.

The eighth, ninth, tenth, eleventh, and twelfth lectures are of a more philosophical character and deal principally with the methods and nature of scientific inquiry. In the ideas summarised in them will be found one of the most important contributions to the theory of knowledge made in the last quarter of a century. Significant hints in psychological method, and exemplary specimen-researches in psychology and physics, are also presented; while in physics many ideas find their first discussion that afterwards, under other names and other authorship, became rallying-cries in this department of inquiry.

All the proofs of this translation have been read by Professor Mach himself.

T. J. MCCORMACK.

LA SALLE, ILL., May, 1898.

TABLE OF CONTENTS.

The Forms of Liquids 1 The Fibres of Corti 17 On the Causes of Harmony 32 The Velocity of Light 48 Why Has Man Two Eyes? 66 On Symmetry 89 On the Fundamental Concepts of Electrostatics 107 On the Principle of the Conservation of Energy 137 On the Economical Nature of Physical Inquiry 186 On Transformation and Adaptation in Scientific Thought 214 On the Principle of Comparison in Physics 236 On the Part Played by Accident in Invention and Discovery 259 On Sensations of Orientation 282 On Some Phenomena Attending the Flight of Projectiles 309 On Instruction in the Classics and the Mathematico-Physical Sciences 338 Appendixes. I. A Contribution to the History of Acoustics 375 II. Remarks on the Theory of Spatial Vision 386 Index 393

THE FORMS OF LIQUIDS.

What thinkest thou, dear Euthyphron, that the holy is, and the just, and the good? Is the holy holy because the gods love it, or are the gods holy because they love the holy? By such easy questions did the wise Socrates make the market-place of Athens unsafe and relieve presumptuous young statesmen of the burden of imaginary knowledge, by showing them how confused, unclear, and self-contradictory their ideas were.

You know the fate of the importunate questioner. So called good society avoided him on the promenade. Only the ignorant accompanied him. And finally he drank the cup of hemlock--a lot which we ofttimes wish would fall to modern critics of his stamp.

What we have learned from Socrates, however,--our inheritance from him,--is scientific criticism. Every one who busies himself with science recognises how unsettled and indefinite the notions are which he has brought with him from common life, and how, on a minute examination of things, old differences are effaced and new ones introduced. The history of science is full of examples of this constant change, development, and clarification of ideas.

But we will not linger by this general consideration of the fluctuating character of ideas, which becomes a source of real uncomfortableness, when we reflect that it applies to almost every notion of life. Rather shall we observe by the study of a physical example how much a thing changes when it is closely examined, and how it assumes, when thus considered, increasing definiteness of form.

The majority of you think, perhaps, you know quite well the distinction between a liquid and a solid. And precisely persons who have never busied themselves with physics will consider this question one of the easiest that can be put. But the physicist knows that it is one of the most difficult. I shall mention here only the experiments of Tresca, which show that solids subjected to high pressures behave exactly as liquids do; for example, may be made to flow out in the form of jets from orifices in the bottoms of vessels. The supposed difference of kind between liquids and solids is thus shown to be a mere difference of degree.

The common inference that because the earth is oblate in form, it was originally fluid, is an error, in the light of these facts. True, a rotating sphere, a few inches in diameter will assume an oblate form only if it is very soft, for example, is composed of freshly kneaded clay or some viscous stuff. But the earth, even if it consisted of the rigidest stone, could not help being crushed by its tremendous weight, and must perforce behave as a fluid. Even our mountains could not extend beyond a certain height without crumbling. The earth may once have been fluid, but this by no means follows from its oblateness.

The particles of a liquid are displaced on the application of the slightest pressure; a liquid conforms exactly to the shapes of the vessels in which it is contained; it possesses no form of its own, as you have all learned in the schools. Accommodating itself in the most trifling respects to the conditions of the vessel in which it is placed, and showing, even on its surface, where one would suppose it had the freest play, nothing but a polished, smiling, expressionless countenance, it is the courtier par excellence of the natural bodies.

Liquids have no form of their own! No, not for the superficial observer. But persons who have observed that a raindrop is round and never angular, will not be disposed to accept this dogma so unconditionally.

It is fair to suppose that every man, even the weakest, would possess a character, if it were not too difficult in this world to keep it. So, too, we must suppose that liquids would possess forms of their own, if the pressure of the circumstances permitted it,--if they were not crushed by their own weights.

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