The investigator should have a robust faith - and yet not believe.

We must alter theory to adapt it to nature, but not nature to adapt it to theory.‎

It is what we know already that often prevents us from learning.

The terrain is everything; the germ is nothing.

Science increases our power in proportion as it lowers our pride.

Mediocre men often have the most acquired knowledge. It is in the darker. It is in the darker regions of science that great men are recognized; they are marked by ideas which light up phenomena hitherto obscure and carry science forward.

Men who have excessive faith in their theories ... make poor observations, because they choose among the results of their experiments only what suits their object, neglecting whatever is unrelated to it and carefully setting aside everything which might tend toward the idea they wish to combat