Not far from the invention of fire we must rank the invention of doubt.

In the world of letters, learning and knowledge are one, and books are the source of both; whereas in science, as in life, learning and knowledge are distinct, and the study of things, and not of books, is the source of the latter.

The science, the art, the jurisprudence, the chief political and social theories, of the modern world have grown out of Greece and Rome-not by favour of, but in the teeth of, the fundamental teachings of early Christianity, to which science, art, and any serious occupation with the things of this world were alike despicable.

I protest that if some great Power would agree to make me always think what is true and do what is right, on condition of being turned into a sort of clock and would up every morning before I got out of bed, I should instantly close with the offer.

The great end of life is not knowledge but action.

Matter and force are the two names of the one artist who fashions the living as well as the lifeless.

Mix salt and sand, and it shall puzzle the wisest of men, with his mere natural appliances, to separate all the grains of sand from all the grains of salt; but a shower of rain will effect the same object in ten minutes.