THE ATOM
AND THE BOHR THEORY
OF ITS STRUCTURE
Original Title:
“Bohr’s Atomteori, almenfatteligt fremstillet”
Translated fromthe Danish by R. B. Lindsay,
Fellow of the American-Scandinavian Foundation,
1923, and Rachel T. Lindsay
THE ATOM AND
THE BOHR THEORY
OF ITS STRUCTURE
An Elementary Presentation
BY
H. A. KRAMERS
LECTURER AT THE INSTITUTE OF THEORETICAL PHYSICS
IN THE UNIVERSITY OF COPENHAGEN
AND
HELGE HOLST
LIBRARIAN AT THE ROYAL TECHNICAL COLLEGE OF COPENHAGEN
WITH A FOREWORD BY
SIR ERNEST RUTHERFORD, F.R.S.
NEW YORK
ALFRED A. KNOPF
1923
PRINTED IN GREAT BRITAIN BY
MORRISON AND GIBB LTD., EDINBURGH
PREFACE
At the close of the nineteenth century and the beginning of thetwentieth, our knowledge of the activities in the interior of matterexperienced a development which surpassed the boldest hopes thatcould have been entertained by the chemists and physicists of thenineteenth century. The smallest particles of chemistry, the atoms ofthe elements, which hitherto had been approached merely by inductivethought, now became tangible realities, so to speak, which could becounted and whose tracks could be photographed. A series of remarkableexperimental investigations, stimulated largely by the Englishphysicist, J. J. Thomson, had disclosed the existence of negativelycharged particles, the so-called electrons, ¹/₂₀₀₀the mass of the smallest atom of the known elements. A theory of electrons,based on Maxwell’s classical electrodynamical theory and developed mainlythrough the labours of Lorentz in Holland and Larmor in England, hadbrought the problem of atomic structure into close connection withthe theory of radiation. The experiments of Rutherford proved, beyonda doubt, that atoms were composed simply of light, negative electricparticles, and small heavy, positive electric particles. The new“quantum theory” of Planck was proving itself very powerful inovercoming grave difficulties in the theory of radiation. The timethus seemed ripe for a comprehensive investigation of the fundamentalproblem of physics—the constitution of matter, and an explanation interms of simple general laws of the physical and chemical properties ofthe atoms of the elements.
During the first ten years of the new century the problem was attackedwith great zeal by many scientists, and many interesting atomic modelswere developed and studied. But most of these had more significance forchemistry than for physics, and it was not until 1913 that the work ofthe Danish physicist, Niels Bohr, paved the way for a really physicalinvestigation of the problem in a remarkable series of papers on thespectrum and atomic structure of hydrogen. The ideas of Bohr, foundedas they were on the quantum theory, were startling and rev