the value of the favor to the rent-seeker; named for American economist Gordon Tullock Twyman's law: "Any figure that looks interesting or different is usually wrong", following the principle that "the more unusual or interesting the data, the more likely they are to have been the result of an error of one kind or another". Van Loon's law: "The amount of mechanical development will always be in inverse ratio to the number of slaves that happen to be at a country's disposal." Named for Hendrik Willem van Loon. Vegard's law, in metallurgy, is an approximate empirical rule which holds that a linear relation exists, at constant temperature, between the crystal lattice parameter of an alloy and the concentrations of the constituent elements. Named for Lars Vegard. Verdoorn's law, in economics: faster growth in output increases productivity due to increasing returns. Named after Dutch economist Petrus Johannes Verdoorn. Verner's law, stated by Karl Verner in 1875, describes a historical sound change in the Proto-Germanic language whereby voiceless fricatives *f, *þ, *s and *x, when immediately following an unstressed syllable in the same word, underwent voicing and became respectively *b, *d, *z and *g. Vierordt's law states that, retrospectively, "short" intervals of time tend to be overestimated, and "long" intervals of time tend to be underestimated. Named after German physician Karl von Vierordt. Vopěnka's principle, in mathematics, is a large cardinal axiom that states that the set-theoretical universe is so large that in every proper class, some members are similar to others, with this similarity formalized through elementary embeddings. Named after Petr Vopěnka. Wagner's law predicts that the development of an industrial economy will be accompanied by an increased share of public expenditure in gross national product, and is named after the German economist Adolph Wagner (1835–1917). Walras's law: budget constraints imply that the values of excess market demands must sum to zero. Weber–Fechner law, named after the Germans Ernst Heinrich Weber and Gustav Theodor Fechner, attempts to describe the human perception of various physical stimuli. In most cases, Stevens's power law gives a more accurate description. Weyl law, in mathematics, describes the asymptotic behavior of eigenvalues of the Laplace-Beltrami operator. Named for Hermann Weyl. The Wiedemann–Franz law, in physics, states that the ratio of the electronic contribution of the thermal conductivity (κ) to the electrical conductivity (σ) of a metal is proportional to the temperature (T). Named for Gustav Wiedemann (1826–1899)