Progress has not followed a straight ascending line, but a spiral with rhythms of progress and retrogression, of evolution and dissolution.

Art is based on a strong sentiment of religion,--on a profound and mighty earnestness; hence it is so prone to co-operate with religion.

This is the highest wisdom that I own; freedom and life are earned by those alone who conquer them each day anew.

We must not take the faults of our youth with us into old age, for age brings along its own defects.

One is never satisfied with the portrait of a person that one knows.

The Christian religion, though scattered and abroad will in the end gather itself together at the foot of the cross.

Should I not be proud, when for twenty years I have had to admit to myself that the great Newton and all the mathematicians and noble calculators along with him were involved in a decisive error with respect to the doctrine of color, and that I among millions was the only one who knew what was right in this great subject of nature?