From Campaign in France in the Year 1792 (1849), by Johann Wolfgang von Goethe.

I spoke of, and have heard it maintained, that a person can escape and save himself from a painful, self-torturing, gloomy state of mind, only by the contemplation of nature, and hearty sympathy with the outward world. Even the most general acquaintance with nature, it does not signify in what way, any active communication with it, either in gardening or farming, hunting or mining, draws us out of ourselves; the employment of mental energies upon real, actual appearances, gives us, by degrees, the greatest satisfaction, clearness, and instruction; just as the artist who keeps true to nature, and, at the same time, goes on cultivating his mind, is certain to succeed the best.