Page:Popular Science Monthly Volume 75.djvu/183

Rh salt? First and foremost an interesting lot of entirely new knowledge. Our understanding of salt has been broadened and deepened. Salt is a much more complex thing to us now than it was before. Instead of simplifying salt by reducing it to its elements, we have greatly complicated it. But notice this particularly: The new knowledge has not enhanced by one jot our knowledge of the physical properties of salt. There is nothing whatever in the properties of the sodium or the chlorine that gives us any clue to the properties of the salt. We might, so far as the best cunning in observation we now possess promises anything, examine the sodium and the chlorine till doomsday and never suspect that together they might produce salt, unless we happened to put them together and note that salt actually did result.

This is a threadbare, school-book story. Why revamp it here? Because it is part, though an essential part, of a much larger story, the whole of which is rarely if ever told. Before we can reach the heart of the matter we must stop a moment with another fact so familiar as likewise to seem stale. Our physical examination of the salt, the sodium and the chlorine, were applications of the general principle that the first step in all knowledge of external objects is the determination of their physical qualities. The familiar expression is, "we know an object only by its properties, or qualities." Let us take this statement from its pigeon-hole of mere habit, and look at it reflectively. Does it mean that there are no natural objects in all the universe about which we can get knowledge in no way other than through their physical properties? Those of you who say "yes, that is what it means," I agree with, and with you might go on at once with the discussion. But some will, I suspect, hesitate to reply thus. To you who hesitate, I say that if there be objects which we may know by other means than through their physical properties, they must be namable, otherwise you could not claim for them a place in the physical world; so I demand that you mention examples. You will probably name the atoms of the chemist and the ether of space. You are then, in so far as concerns the atoms, committed to the conception of propertyless atoms, are you not? I ask you to tell me then exactly what it was that John Dalton and the other founders of modern chemistry actually did. Certainly there were atomic theories of the constitution of matter long before these men lived. Democritus and Newton, to say nothing of others, made much of such atoms. Why did the pre-Daltonian atoms signify nothing, or almost nothing for physical science? Because they were propertyless atoms. To attach to these old purely speculative, and hence scientifically useless atoms, one property of the particular substance to which they belong, was exactly what these chemists did. The property so attached was that of combining with other substances in definite ways.

Analyze the atomic theory of modern chemistry and you will find