Apart from the alchemists' belief in the analogy between natural and spiritual things, it is, I think, incredible that any such theories of the metals and the possibility of their transmutation or "regeneration" by such an extraordinary agent as the Philosopher's Stone would have occurred to the ancient investigators of Nature's secrets. When they had started to formulate these theories, facts(1) were discovered which appeared to support them; but it is, I suggest, practically impossible to suppose that any or all of these facts would, in themselves, have been sufficient to give rise to such wonderfully fantastic theories as these: it is only from the standpoint of the theory that alchemy was a direct offspring of mysticism that its origin seems to be capable of explanation. (1) One of those facts, amongst many others, that appeared to confirm the alchemical doctrines, was the ease with which iron could apparently be transmuted into copper. It was early observed that iron vessels placed in contact with a solution of blue vitriol became converted (at least, so far as their surfaces were concerned) into copper. This we now know to be due to the fact that the copper originally contained in the vitriol is thrown out of solution, whilst the iron takes its place. And we know, also, that no more copper can be obtained in this way from the blue vitriol than is actually used up in preparing it; and, further, that all the iron which is apparently converted into copper can be got out of the residual solution by appropriate methods, if such be desired; so that the facts really support DALTON'S theory rather than the alchemical doctrines. But to the alchemist it looked like a real transmutation of iron into copper, confirmation of his fond belief that iron and other base metals could be transmuted into silver and gold by the aid of the Great Arcanum of Nature.