generally, of the physical and the psychological worlds(1). Fechner developed the concept of estimating or measuring the magnitude of sensations by assigning numerical values, reasoning that the relative magnitudes of sensations would be mathematically related to the magnitudes of the corresponding physical stimuli. In the years since Fechner's work, psychophysicists have endeavored to establish the laws relating physical stimuli to the resulting conscious sensations of the human observer. These efforts have concerned the responses of subjects to a number of basic questions about physical stimuli. Referring specifically to odors, these questions and the types of sensory evaluation needed to answer them can be tabulated(Table 17.1