These considerations were entirely unknown to the great controversialists of a generation ago; but there is another order of facts, entirely unimagined by them, which are now demonstrable and admitted. For them, or for most of them, the ancient conception of matter which we trace to Plato was substantially true; nay, more. The recent work of the physicists and chemists had endowed that ancient conception of matter as gross and inert and dead with a new concreteness and vividness. One of the greatest physicists of the age, James Clerk-Maxwell, in his famous address to the British Association, spoke of atoms as the “foundation stones of the visible universe, which have existed since the creation unbroken and unworn.” The accepted conception of an atom was that of a passive thing; it had its own inherent shape and properties, which were impressed upon it at its creation. It had “the stamp of the manufactured article,” as Sir John Herschell said, and throughout its endless history it responded to and behaved under the influence of external forces in due accordance with its shape and size. But it was unchangeable, inert and brute, the sport of its surroundings, like the mote in the sun-beam. [Sidenote: Immeasurable Ocean of Energy] But to-day we stand amazed at such conceptions. We have learnt that within the atoms of matter there is a fund of energy so incalculably vast that the sum total of all the energies previously recognised, and now to be styled extra-atomic, is as nothing compared with it. This is a change indeed, that all the energies hitherto known to us should be merely the overflow trickling from the immeasurable ocean of the intra-atomic energy, the very existence of which has been formally and repeatedly denied by practically all thinkers from Plato down to our own time. Matter is not gross and inert, brute and dead. The atom, the so-called unchangeable foundation stone, is, on the contrary, itself an organism, the theatre of Titanic forces about which we at present know practically nothing except that they certainly exist, and are powerful beyond all our previous conceptions. The atom is no atom, but a microcosm; it is no more the unit of inorganic matter than the cell is really the unit of living matter.