 Fechner’s claims concerning the measurability of sensation became the subject of a series of debates that lasted nearly a century and proved extremely fruitful for the philosophy of measurement, involving key figures such as Mach, Helmholtz, Campbell and Stevens (Heidelberger 1993a: Ch. 6 and 1993b; Michell 1999: Ch. 6). Those objecting to the measurability of sensation, such as Campbell, stressed the necessity of an empirical concatenation operation for fundamental measurement. Since intensities of sensation cannot be concatenated to each other in the manner afforded by lengths and weights, there could be no fundamental measurement of sensation intensity. Moreover, Campbell claimed that none of the psychophysical regularities discovered thus far are sufficiently universal to count as laws in the sense required for derived measurement (Campbell in Ferguson et al. 1940: 347). All that psychophysicists have shown is that intensities of sensation can be consistently ordered, but order by itself does not yet warrant the use of numerical relations such as sums and ratios to express empirical results.