My days I devote to reading and experiments in chemistry, and I spend many of the clear nights in the study of astronomy. There is, though I do not know how there is or why there is, a sense of infinite peace and protection in the glittering hosts of heaven. There it must be, I think, in the vast and eternal laws of matter, and not in the daily cares and sins and troubles of men, that whatever is more than animal within us must find its solace and its hope.

If anything is possible, then nothing is interesting

Losing your way on a journey is unfortunate. But, losing your reason for the journey is a fate more cruel.

If we do not end war - war will end us. Everybody says that, millions of people believe it, and nobody does anything.

What, unless biological science is a mass of errors, is the cause of human intelligence and vigour? Hardship and freedom: conditions under which the active, strong, and subtle survive and the weaker go to the wall; conditions that put a premium upon the loyal alliance of capable men, upon self-restraint, patience, and decision. And the institution of the family, and the emotions that arise therein, the fierce jealousy, the tenderness for offspring, parental self-devotion, all found their justification and support in the imminent dangers of the young.

Non-violence is the policy of the vegetable kingdom.

Nothing leads so straight to futility as literary ambitions without systematic knowledge.