Psychology considered as a natural science began as Aristotelian “physics” or “natural philosophy” of the soul. C. Wolff placed psychology under metaphysics, coordinate with cosmology. Near the middle of the eighteenth century, Krueger, Godart, and Bonnet proposed approaching the mind with the techniques of the new natural science. At nearly the same time, Scottish thinkers placed psychology within moral philosophy, but distinguished its “physical” laws from properly moral laws (for guiding conduct). British and French visual theorists developed mathematically precise theories of size and distance perception; they created instruments to test these theories and to measure visual phenomena such as the duration of visual impressions. By the end of the century there was a flourishing discipline of empirical psychology in Germany, with professorships, textbooks, and journals. The practitioners of empirical psychology at this time typically were dualists who included mental phenomena within nature.