PSYCHOPHYSICS (from Gr. ifivXil, soul, 4uvcs, nature)  , a department of psychology which deals with the physiological aspects of mental phenomena, and in particular investigates the quantitative relations between stimuli and the resultant sensations . Following the introspective school of which the last leader was Alexander Bain, the tendency of psychological investigation, in the hands of Fechner, Helmholtz, Wundt, Munsterberg, was predominantly psychophysical, and psycho-logical study, especially in Germany, where the first fully-equipped laboratory was set up in Leipzig (1879) by Wundt, and in America became largely a matter of experiment and apparatus . Such apparatus has been devised for optical, acoustical, haptical (Gr . Cis-rev, touch), taste and smell experiments . Haptical apparatus includes the kinesimeter (for cutaneous sensation), the thermaesthesiometer (for heat and cold sensation), the algometer or algesimeter (for pain sensations), the aesthesiometer (e.g. those of Jastrow and Munsterberg) . Among important apparatus for measuring the time relations of mental processes are the d'Arsonval chronometer, which marks hundredths of a second, and the Hipp chronoscope, in which the stimulus and, the clock are electrically connected . For authorities see Baldwin's Dict. of Philos. and Psych. s.v . " Laboratory," and the latest psychological textbooks .