The practice of using a physical object upon which to gaze in order to concentrate attention during meditation makes it much easier for those who are attracted to it. A metaphysician of Konigsberg, Immanuel Kant, used the same practice when working out his metaphysical theories. Sitting in his study, he would look through the window and fix his sight on a particular fir tree which was growing outside. One day it was cut down and removed and for some time thereafter Kant found difficulty in holding his line of thought without the accustomed fir tree to gaze upon. Indeed, Kant was such a creature of habit that every evening punctually at five o'clock he would take his walk. People in the city of Konigsberg used to time their watches by his appearance in the street, because he was invariably punctual in starting his walk.
-- Notebooks Category 4: Elementary Meditation > Chapter 3 : Fundamentals > # 137
