Gustav Theodor Fechner (1801 – 1887) was a German physicist and philosopher, known as the founder of psychophysics. Fechner extended on the work of Ernst Weber, and attempted to define laws describing the relationship between physical stimuli and mental representations of those stimuli. Fechner formulated what he called Weber’s law (now known as Fechner’s law), based on the experimental work of Weber.

Source:

Kantowitz, B. H., Roediger H. L., Elmes, D. G. (2008). Experimental Psychology (Ninth Edition). (pp.436-437) Belmont, CA: Wadsworth, Cengage Learning