I give them experiments and they respond with speeches.

If it is a terrifying thought that life is at the mercy of the multiplication of these minute bodies [microbes], it is a consoling hope that Science will not always remain powerless before such enemies.

Preconceived ideas are like searchlights which illumine the path of the experimenter and serve him as a guide to interrogate nature. They become a danger only if he transforms them into fixed ideas-this is why I should like to see these profound words inscribed on the threshold of all the temples of science: 'The greatest derangement of the mind is to believe in something because one wishes it to be so.'

To bring one's self to believe in a truth that has just dawned upon one is the first step towards progress; to persuade others is the second.

Do not promote what you can't explain, simplify, and prove early.

Without theory, practice is but routine born of habit. Theory alone can bring forth and develop the spirit of inventions.

The grandeur of the acts of men are measured by the inspiration from which they spring.