Imagination should give wings to our thoughts but we always need decisive experimental proof, and when the moment comes to draw conclusions and to interpret the gathered observations, imagination must be checked and documented by the factual results of the experiment.

After death, life reappears in a different form and with different laws. It is inscribed in the laws of the permanence of life on the surface of the earth and everything that has been a plant and an animal will be destroyed and transformed into a gaseous, volatile and mineral substance.

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.

The greatest derangement of the mind is to believe in something because one wishes it to be so.

Without theory, practice is but routine born of habit. Theory alone can bring forth and develop the spirit of invention. ... [Do not] share the opinion of those narrow minds who disdain everything in science which has not an immediate application. ... A theoretical discovery has but the merit of its existence: it awakens hope, and that is all. But let it be cultivated, let it grow, and you will see what it will become.

One does not ask of one who suffers: What is your country and what is your religion? One merely says: You suffer, that is enough for me.

The nights seem to me too long... I am often scolded by Madame Pasteur, but I tell her I shall lead her to fame.