The greatest evil that can befall man is that he should come to think ill of himself.
The errors of the observer come from the qualities of the human mind.
Truth must be repeated again and again, because error is constantly being preached round about.
Every solution of a problem is a new problem.
Words are mere sound and smoke, dimming the heavenly light.
You acquire a language most readily in the country where it is spoken; you study mineralogy best among miners; and so with everything else.