In 1861 Wilhelm Wundt conducted an experiment on reaction time, which was a turning point in the field of psychology. Using a pendulum that hit a bell upon reaching its outer limits, Wundt demonstrated a 10th of a second delay between hearing the bell and noting the position of the pendulum (and vice versa), and it was during that very brief period that a mental process occurred. Finally, activities of the mind could be measured (Thorne & Henley, 2005).
Archives of the History of American Psychology, The Center for the History of Psychology, The University of Akron