The man of science, when he wishes others to see what he has seen, arranges his microscope or telescope ; that is to say, he makes changes in the external world, but demands of the observer only normal eyesight. The mystic, on the other hand, demands changes in the observer, by fasting, by breathing exercises, and by a careful abstention from external observation.
Source: Religion and Science, 1935, chapt. 7
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