My interest in science was always essentially limited to the study of principles.... That I have published so little is due to this same circumstance, as the great need to grasp principles has caused me to spend most of my time on fruitless pursuits.

Try first to be a man of value; success will follow.

Long live impudence. It was my guardian angel in this world.

The point is to develop the childlike inclination for play and the childlike desire for recognition and to guide the child over to important fields for society. Such a school demands from the teacher that he be a kind of artist in his province.

It is impossible to get anywhere without sinning against reason.

The process of scientific discovery is, in effect, a continual flight from wonder.

(Reply on what constitutes scientific proof:)"The question is much too difficult for me.