A man’s life may stagnate as literally as water may stagnate, and just as motion and direction are the remedy for one, so purpose and activity are the remedy for the other.

Nature is not benevolent; Nature is just, gives pound for pound, measure for measure, makes no exceptions, never tempers her decrees with mercy, or winks at any infringement of her laws.

Joy in the universe, and keen curiosity about it all - that has been my religion.

If we take science as our sole guide, if we accept and hold fast that alone which is verifiable, the old theology must go.

Natural history is a matter of observation; it is a harvest which you gather when and where you find it growing. Birds and squirrels and flowers are not always in season, but philosophy we have always with us. It is a crop which we can grow and reap at all times and in all places and it has its own value and brings its own satisfaction.

[T]he cold warms me—after a different fashion from that of the kitchen stove.

When nature made the blue-bird she wished to propitiate both the sky and the earth, so she gave him the color of the one on his back and the hue of the other on his breast.