He also coined the word "agnostic," to describe his own religious idea that the only things worth believing in were things that could be directly observed in the world. His definition:
Positively the principle may be expressed: In matters of your intellect, follow you reason as far as it will take you, without regard to any other consideration. And negatively: In matters of the intellect, do not pretend that conclusions are certain which are not demonstrated or demonstrable. That I take to be the agnostic faith, which if a man keep whole and undefiled, he shall not be ashamed to look the universe in the face, whatever the future may have in store for him.
Wonder FCD; FTH