Each class of substances, they said, has a life, or spirit (an essential character, we might say) of its own.

"The life of sulphur," Paracelsus said, "is a combustible, ill-smelling, fatness....

The life of gems and corals is mere colour....

The life of water is its flowing....

The life of fire is air." Grant an attraction of like to like, and the reason becomes apparent for such directions as these: "Nothing heterogeneous must be introduced into our magistery"; "Everything should be made to act on that which is like it, and then Nature will perform her duty." Although each class of substances was said by the alchemists to have its own particular character, or life, nevertheless they taught that there is a deep-seated likeness between all things, inasmuch as the power of _the essence_, or _the one thing_, is so great that under its influence different things are produced from the same origin, and different things are caused to pass into and become the same thing.
In _The New Chemical Light_ it is said: "While the seed of all things is one, it is made to generate a great variety of things." It is not easy now--it could not have been easy at any time--to give clear and exact meanings to the doctrines of the alchemists, or the directions they gave for performing the operations necessary for the production of the object of their search.