I have been speculating last night what makes a man a discoverer of undiscovered things. As far as I can conjecture the art consists in habitually searching for the causes and meaning of everything which occurs.

We feel surprise when travellers tell us of the vast dimensions of the Pyramids and other great ruins, but how utterly insignificant are the greatest of these, when compared to these mountains of stone accumulated by the agency of various minute and tender animals!

I am not very sceptical, — a frame of mind which I believe to be injurious to the progress of science. A good deal of scepticism in a scientific man is advisable to avoid much loss of time, but I have met with not a few men, who, I feel sure, have often thus been deterred from experiment or observations, which would have proved directly or indirectly serviceable .

When primeval man first used flint stones for any purpose, he would have accidentally splintered them, and would then have used the sharp fragments. From this step it would be a small one to break the flints on purpose and not a very wide step to fashion them rudely.

[Alexander von Humboldt was the] greatest scientific traveller who ever lived.

Blushing is the most peculiar and the most human of all expressions. Monkeys redden from passion, but it would require an overwhelming amount of evidence to make us believe that any animal could blush.

Multiply, vary, let the strongest live and the weakest die.