Nor did the word _transmutation_ mean to the alchemist what it means to the chemist.
The facts which are known at present concerning the elements make unthinkable such a change as that of lead into silver; but new facts _may_ be discovered which will make possible the separation of lead into things unlike itself, and the production of silver by the combination of some of these constituents of lead.

The alchemist supposed he knew such facts as enabled him not only to form a mental picture of the change of lead into silver, or tin into gold, but also to assert that such changes must necessarily happen, and to accomplish them.

Although we are quite sure that the alchemist's facts were only imaginings, we ought not to blame him for his reasoning on what he took to be facts.
Every metal is now said to be an element, in the modern meaning of that word: the alchemist regarded the metals as composite substances; but he also thought of them as more simple than many other things.
Hence, if he was able to transmute one metal into another, he would have strong evidence in support of his general conception of the unity of all things.

And, as transmutation meant, to the alchemist, the bringing of a substance to the condition of greatest perfection possible for that substance, his view of the unity of nature might be said to be proved if he succeeded in changing one of the metals, one of these comparatively simple substances, into the most perfect of all metals, that is, into gold.
The transmutation of the baser metals into gold thus came to be the practical test of the justness of the alchemical scheme of things.
Some alchemists assert they had themselves performed the great transmutation; others tell of people who had accomplished the work.
The following story is an example of the accounts given of the making of gold.

It is taken from _John Frederick Helvetius' Golden Calf, which the world worships and adores_ (17th century):-- "On the 27th December 1666, in the forenoon, there came to my house a certain man, who was a complete stranger to me, but of an honest grave countenance, and an authoritative mien, clothed in a simple garb....