 At the same time, however, progress was being made in human physiology, especially of the sensory systems. In 1834, the physiologist, E.H. Weber, published a startling discovery in his De tactu. His experiments on the sensation of weight had led him to find that there obtains a constant ratio between, on the one hand, a given stimulus and, on the other hand, a second stimulus sufficiently larger for the difference between the two stimuli to be just noticeable, no matter the magnitude of the first  stimulus.[12]  In other words, if the first stimulus is of intensity \(I\), then \(\Delta I\) is the amount by which it must be increased for the difference to be just noticeable; the ratio of \(I\) and \(\Delta I\) is constant (\(k\)): \(\Delta I / I = k\) (cf. L III: 186). This equation, which later came to be known as Weber’s  Law,[13]  was crucial to the development of psychology because it apparently demonstrated that where Herbart had failed in his aprioristic construction of mathematical regularities of mind, experimentation could succeed. The situation nevertheless remained murky as interpretations of Weber’s Law multiplied. Fechner, for example, elaborated Weber’s experiments but took his results as the basis for an arcane panpsychic monism (Wundt’s own “psychological” interpretation is treated in  Section 4)  (cf., e.g., Boring 1950: 286).