John Muir (2015). “JOHN MUIR’S CALIFORNIA COLLECTION: My First Summer in the Sierra, Picturesque California, The Mountains of California, The Yosemite & Our National Parks (Illustrated): Adventure Memoirs, Travel Sketches, Nature Writings and Wilderness Essays”, p.276, e-artnow
Soren Kierkegaard's letter to Henriette Kierkegaard (1847), as quoted in Soren Kierkegaard "Letters and Documents" (translated by Henrik Rosenmeier), www.huffingtonpost.com. 1978.