In the present chapter we examine the first three centuries of Greek scientific progress; our period begins with the earliest impact of oriental scientific ideas on Ionian Greece, and ends with the conquest of Greece by Alexander the Great (332 b.c.), the death of Aristotle (322 b.c.), a general decline of science and art in Greece, and the foundation of the City of Alexandria and of its university (323 b.c.), which was to be the intellectual centre of the world for many generations to come. In brief, we study Greek science in the period of Greece's intellectual greatness.

This science was almost entirely mathematical. The Greeks had nothing of our elaborate equipment of laboratories and observatories. Indeed, their equipment was limited to their own brains, but these were of the very best; just as Aeschylus and Sophocles exhibit mental powers comparable with those of Shakespeare, so Archimedes and Aristarchus exhibit powers comparable with those of Newton. Thus they could attack their various problems only by reflection and contemplation, aided at most by a minimum of observation, and when physics and astronomy creep in, it is in the form of philosophical speculation rather than of true science as we understand it to-day.

It will be convenient to discuss the early Greek mathematics, physics and astronomy separately, and in this order.

We now approach an era which, if not so strikingly brilliant as its great predecessor, was at least one of solid and steady progress. It produced no second Newton, but provided an abundance of first-class investigators. The studious and talented amateur could still accomplish scientific work of the highest value, for a single mind could carry a good working knowledge of a substantial part of science; the days of immense stacks of literature and teams of experts, each understanding only one corner of a subject of research, had not yet arrived. They were, however, on the way, for there was already a tendency for the various sciences to unite into one, to lose their identity as detached units, and become merged into one single field of knowledge which was too vast for anyone to comprehend the whole, or even a large fraction of it. We note the appearance of such words as thermodynamics, astrophysics and electrochemistry.

MECHANICS

Mechanics looms large in the story of eighteenth-century progress. Galileo and Newton had opened the road, but a lot remained to be done in extending their gains and filling up lacunae. Newton's laws of motion were applicable only to particles, i.e. to pieces of matter which were small enough to be treated as points, and so could have definite positions, velocities and accelerations unambiguously assigned to them.

There are a vast number of detailed and comprehensive histories, both of general science and of special departments of science. Most of these are admirable for the scientific reader, but the layman sometimes cannot see the wood for the trees. I have felt no ambition (nor competence) to add to their number, but have thought I might usefully try to describe the main lines of advance of physical science, including astronomy and mathematics but excluding all points and side-issues, in language non-technical enough to be understood by readers who have no scientific attainments or knowledge.

I hope that such a book may prove of interest to the general educated reader, perhaps also to those who are beginning the study of physics, and possibly to students of other subjects who wish to know something of how physical science has grown, what it has done, and what it can do.

The two centuries from 1687 to 1887 may appropriately be described as the mechanical age of physics. Science seemed to have found that we lived in a mechanical world, a world of particles which moved as the forces from other particles made them move, a world in which the future is completely determined by the past. In 1687 Newton's Principia had interpreted the astronomical universe very successfully in this way. Before 1887 Maxwell had interpreted radiation in an essentially similar way, teaching that it consisted of disturbances travelling through an ether under the direction of mechanical laws. Finally, in 1887 Hertz produced radiation of Maxwellian type from electric sources in the laboratory, and demonstrated its similarity to ordinary light. This seemed to fit a final keystone into the structure which had been built up in the preceding two centuries.

Most physicists now thought of this structure as standing foursquare, complete and unshakable. It was hard to imagine the physicists of the future finding any more exciting occupation than dotting the i's and crossing the t's of the mechanical explanation of the universe, and carrying the measurement of physical quantities to further decimal places.

Little did anyone imagine how completely different the actual course of events would be. Yet the year 1887, which had provided a keystone to the structure, also saw the structure begin visibly to totter; it was the year of the famous Michelson-Morley experiment, which first showed that there was something wrong with the foundations.

Here and there, in the history of human thought and action, we find periods to which the epithet ‘great’ may properly be applied—in Greece the fourth century before Christ; in England the Elizabethan age; in the domain of science the seventeenth century, the ‘century of genius’, to which we now come.

It would be very undiscerning to suppose that such a period of greatness could arrive as a mere accident, a specially brilliant galaxy of exceptional minds just happening to be born at one particular epoch. Mental ability is believed to be transmitted in accordance with the laws of heredity, in which case the laws of probability will see to it that no abrupt jump occurs from one generation to the next. Thus a period of greatness must be attributed to environment rather than to accident; if an age shows one particular form of greatness, external conditions must have encouraged that form. For instance, the sixteenth century was an age of great explorers because conditions then specially favoured exploration; the pioneering voyages of Columbus, Vasco da Gama, Cabot, Magellan and others had drawn attention to the wealth of new territory awaiting discovery, while men had learned to build ships which could defy the worst fury of the ocean.