For instance, there is hardly any end to the developments we might allow ourselves to imagine as arising out of the new theories, still in a probationary condition, as to the ultimate physical structure of the universe. Such conjectures might be followed indefinitely in several directions, and the resulting conclusions would be more likely to err by timidity than by extravagance: but as there is no knowledge at present available which could serve as a guide to the probably-right, and as a warning against the probably-wrong, directions, it would be neither interesting nor useful to pursue them. Radium "the revealer," as Dr Saleeby has called it in one of those brilliant papers which fine imagination and delicate fancy have adorned with many another noble phrase and memorable image, opens the door to a whole world of new possibilities. Our whole conception of cosmic processes may have to be remodelled, in the light of those tiny scintillations which the spinthariscope has popularised. Already our notions concerning the nature of matter have been revolutionised. We are told that atoms, regarded hitherto as the ultimate units of matter--so small that Lord Kelvin has calculated that if a drop of water were magnified to the size of the earth the atoms in it would be somewhere between the size of small shot and the size of cricket balls--are themselves made up of a stuff so almost infinitely more tenuous, that the particles of it within the atom are, relatively to their size, farther apart than the planets of the solar system. Nor is this all. These particles, commonly called electrons, if particles they can still be designated at all, were at first said to "carry" a charge of electricity. But it now seems that they are electricity itself. If this be true, we should seem to be on the point of bridging the void between what used to be called the eternal antithetics--matter and force: and whither this will lead us can only with the greatest caution be pre-imagined. In any case the consequences of this discovery, philosophical as well as scientific, are stupefying in the possibilities they open up to the thinker as well as to the man of practical science. At last science begins to join hands with philosophy. What will be the philosophy of a hundred years hence, imagination pales before the effort of attempting to conceive.