These are the three voices of Nature. She joins hands with us; and says Struggle, Endeavor. She comes close to us, we hear her heart beating; she says Wonder, Enjoy, Revere. She whispers secrets to us, we cannot always catch her words; she says Search, Enquire. These three voices appeal to Hand and Heart and Head, to the trinity of our being.
The System of Animate Nature: The Gifford Lectures Delivered in the, University of St. Andrews in the Years 1915 and 1916 (Volume 2), Lecture XX (p. 648)