BOOK REVIEW 65
lies a complex of intricacies and dramatic events, an understanding of which is essential to demystify science. The task of adding to the content of scientific knowledge is arduous and the path traversed by those who do this job is tortuous. The succinct history of one of the major revolutions in physical sciences, told by Danin with compassion, underscores "science is a human enterprise. In the crucial period of its history the quarrels between logic and imagination are very similar to those happening in every day life-—"
In 1900, when Planck postulated that radiation or energy is transferred discretely in quanta, he had only considered it as a "mathematical technique". Steeped in the classical tradition, he was not at all prepared to renounce the principle of continuity in physical processes. Bohr rather strongly summed up Planck's attitude to his own discovery: "In some sense it can be said that he used the last forty years of his life, not to say fifty, to try to get his discovery out of the world."
In 1905 Einstein carried Planck's idea to its logical conclusion when he argued that radiation was not only exchanged in discontinuous packets but it actually existed in discontinuous packets. Beam of light comprised not a smooth flood of electromagnetic energy but consisted of separate wave packets known as photons.
As against Planck, for whom the theory of quanta remained a source of continuing torment, Einstein, despite his very strong reservations and opposition to the direction of development of quantum mechanics in the following years, had observed: "One cannot regard a concept as senseless only because it differs from classical physics."
Basing himself on the idea of quantum of action, Niels Bohr suggested a theory of the atomic structure that took physics conclusively beyond the limits of classical theory. Acording to the Rutherford-Bohr model of the atom, every atom was occupied by a heavy, positively charged nucleus around which electrons revolve, like planets moving in definite orbits. The 'puzzling* feature of Bohr's theory was that the orbits in which the electrons could revolve were discrete. Bohr^s model had the unclassical feature of forbidding electrons from emitting light when revolving in the allowed orbits. When the electron drops from some higher orbit to the lowest of the allowed orbits, only then does the atom emit a quantum of light. The electrons revolved around the nucleus according to the laws of classical mechanics but between these orbits they emitted light according to the quantum laws of Planck.
Having recommended Bohr's paper for publication, Rutherford wrote to Bohr: "Your ideas as to the mode of origin of spectra in hydrogen are very ingenious and seem to work out well; but the mixture of Planck's ideas with the old mechanics makes it very difficult to form a physical idea of what is the basis of it all."
Such was the conceptual chaos in those days in the world of physics that Lord Rayleigh, sixty then, said that he would not take part in