Part 1

Transcriber’s Notes:

Underscores before and after a word or phrase indicate italics_ in the original text. Equal signs = before and after a word or phrase indicate =bold= in the original text. Small capitals have been converted to SOLID capitals. Illustrations have been moved so they do not break up paragraphs. Deprecated spellings have been preserved. Typographical and punctuation errors have been silently corrected. The list of works by John Tyndall has been moved from the front to the end of the file.

POPULAR LECTURES ON SCIENTIFIC SUBJECTS

BY HERMANN VON HELMHOLTZ

TRANSLATED BY E. ATKINSON, PH.D., F.C.S. FORMERLY PROFESSOR OF EXPERIMENTAL SCIENCE, STAFF COLLEGE

SECOND SERIES

WITH AN AUTOBIOGRAPHY OF THE AUTHOR

LONGMANS, GREEN, AND CO. 39 PATERNOSTER ROW, LONDON NEW YORK, BOMBAY, AND CALCUTTA 1908

All rights reserved

BIBLIOGRAPHICAL NOTE.

Issued in Silver Library, March 1893; Reprinted July 1895, May 1898, June 1900, December 1903, August 1908.

PREFACE.

The favour with which the first series of Professor Helmholtz’s Lectures has been received would justify, if a justification were needed, the publication of the present volume.

I have to express my acknowledgments to Professor G. Croome Robertson, the editor, and to Messrs. Macmillan, the publishers of ‘Mind,’ for permission to use a translation of the paper on the ‘Axioms of Modern Geometry’ which appeared in that journal.

The article on ‘Academic Freedom in German Universities’ contains some statements respecting the Universities of Oxford and Cambridge to which exception has been taken. These statements were a fair representation of the impression produced on the mind of a foreigner by a state of things which no longer exists in those Universities, at least to the same extent. The reform in the University system, which may be said to date from the year 1854, has brought about so many alterations both in the form and in the spirit of the regulations, that older members of the University have been known to speak of the place as so changed that they could scarcely recognise it. Hence, in respect of this article, I have availed myself of the liberty granted by Professor Helmholtz, and have altogether omitted some passages, and have slightly modified others, which would convey an erroneous impression of the present state of things. I have also on these points consulted members of the University on whose judgment I think I can rely.

In other articles, where the matter is of prime importance, I have been anxious faithfully to reproduce the original; nor have I in any such cases allowed a regard for form to interfere with the plain duty of exactly rendering the author’s meaning.

E. ATKINSON.

PORTESBERY HILL, CAMBERLEY: Dec. 1880.

CONTENTS.

LECTURE PAGE I. GUSTAV MAGNUS. IN MEMORIAM 1 II. ON THE ORIGIN AND SIGNIFICANCE OF GEOMETRICAL AXIOMS 27 III. ON THE RELATION OF OPTICS TO PAINTING 73 I. Form 78 II. Shade 94 III. Colour 110 IV. Harmony of Colour 124 IV. ON THE ORIGIN OF THE PLANETARY SYSTEM 139 V. ON THOUGHT IN MEDICINE 199 VI. ON ACADEMIC FREEDOM IN GERMAN UNIVERSITIES 237 VII. HERMANN VON HELMHOLTZ. AN AUTOBIOGRAPHICAL SKETCH 266

GUSTAV MAGNUS.

In Memoriam.

Address delivered in the Leibnitz meeting of the Academy of Sciences on July 6, 1871.

The honourable duty has fallen on me of expressing in the name of this Academy what it has lost in Gustav Magnus, who belonged to it for thirty years. As a grateful pupil, as a friend, and finally as his successor, it was a pleasure to me as well as a duty to fulfil such a task. But I find the best part of my work already done by our colleague Hofmann at the request of the German Chemical Society, of which he is the President. He has solved the difficulty of giving a picture of the life and work of Magnus in the most complete and most charming manner. He has not only anticipated me, but he stood in much closer and more intimate personal relation to Magnus than I did; and, on the other hand, he is much better qualified than I to pronounce a competent judgment on the principal side of Magnus’s activity, namely, the chemical.

Hence what remains for me to do is greatly restricted. I shall scarcely venture to speak as the biographer of Magnus, but only of what he was to us and to science, to represent which is our allotted task.

His life was not indeed rich in external events and changes; it was the peaceful life of a man who, free from the cares of outer circumstances, first as member, then as leader of an esteemed, gifted, and amiable family, sought and found abundant satisfaction in scientific work, in the utilisation of scientific results for the instruction and advantage of mankind. Heinrich Gustav Magnus was born in Berlin on May 2, 1802, the fourth of six brothers, who by their talents have distinguished themselves in various directions. The father, Johann Matthias, was chief of a wealthy commercial house, whose first concern was to secure to his children a free development of their individual capacity and inclinations. Our departed friend showed very early a greater inclination for the study of mathematics and natural philosophy than for that of languages. His father arranged his instruction accordingly, by removing him from the Werder Gymnasium and sending him to the Cauer Private Institute, in which more attention was paid to scientific subjects.

From 1822 to 1827 Magnus devoted himself entirely to the study of natural science at the University of Berlin. Before carrying out his original intention of qualifying as a professor of technology, he spent two years with that object in travelling; he remained with Berzelius a long time in Stockholm, then with Dulong, Thénard and Gay-Lussac in Paris. Unusually well prepared by these means, he qualified in the University of this place in technology, and afterwards also in physics; he was appointed extraordinary professor in 1834, and ordinary professor in 1845, and so distinguished himself by his scientific labours at this time, that nine years after his habilitation, on January 27, 1840, he was elected a member of this Academy. From 1832 until 1840 he taught physics in the Artillery and Engineering School; and from 1850 until 1856 chemical technology in the Gewerbe Institut. For a long time he gave the lectures in his own house, using his own instruments, which gradually developed into the most splendid physical collection in existence at that time, and which the State afterwards purchased for the University. His lectures were afterwards given in the University, and he only retained the laboratory in his own house for his own private work and for that of his pupils.

His life was passed thus in quiet but unremitting activity; travels, sometimes for scientific or technical studies, sometimes also in the service of the State, and occasionally for recreation, interrupted his work here from time to time. His experience and knowledge of business were often in demand by the State on various commissions; among these may be especially mentioned the part he took in the chemical deliberations of the Agricultural Board (Landes-Economie Collegium), to which he devoted much of his time; above all to the great practical questions of agricultural chemistry.