THE ATOMIC THEORY
The theory that matter in spite of its apparent continuity is in reality made up of a great number of very small particles, is as old as the science of Physics itself, and was enunciated almost as soon as men began to reason about physical phenomena. It would, however, be misleading to suppose that there is any very close connexion between the modern Atomic Theory and the views of Democritus and Lucretius. The old theory was in intention and effect metaphysical rather than physical, theological rather than scientific. The physics of two thousand years ago was far too scanty and uncertain to afford any support or test for such a theory; indeed, if I were called upon to prove to you that Democritus was right when he held that matter was discontinuous, and Aristotle wrong when he said it was not so, I should have to appeal to facts not one of which was known either to Democritus or Aristotle. The great and invaluable service which the Greek atomists have rendered to science is that they were the first to attempt on mechanical principles to explain complicated physical phenomena as the result of combinations of simpler ones; they pointed out the goal which science is still struggling to reach. For two thousand years the Atomic Theory itself made no progress, because, though in form a physical theory, it had no real connexion with physical phenomena, no facts were known by which it could be tested, and it was too vague to suggest for itself effects which could be put to the test of experiment. It was sterile because it was divorced from experience. It affords a striking
