gases in metals. Named after German chemist Adolf Sieverts (1874–1947). Smeed's law is an empirical rule relating traffic fatalities to traffic congestion as measured by the proxy of motor vehicle registrations and country population. After R. J. Smeed. Snell's law is the simple formula used to calculate the refraction of light when travelling between two media of differing refractive index. It is named after one of its discoverers, Dutch mathematician Willebrord van Roijen Snell (1580–1626). Sowa's law of standards: "Whenever a major organization develops a new system as an official standard for X, the primary result is the widespread adoption of some simpler system as a de facto standard for X." Spearman's hypothesis: The magnitudes of the black–white differences on tests of cognitive ability positively correlate with the tests' g-loading. Spearman's law of diminishing returns states that the g factor decreases in predictive power for high IQs. Stang's law, in Proto-Indo-European phonology: when a word ends with a vowel followed by a laryngeal or a semivowel *y or *w followed by a nasal, the laryngeal or semivowel is dropped, with compensatory lengthening of a preceding vowel. Named after Norwegian linguist Christian Stang. Stark–Einstein law: every photon that is absorbed will cause a (primary) chemical or physical reaction. Named after Johannes Stark and Albert Einstein. Stefan–Boltzmann law: The total energy radiated per unit surface area of a black body in unit time is directly proportional to the fourth power of the black body's thermodynamic temperature. Named for Jožef Stefan (1835–1893) and Ludwig Boltzmann. Stein's law: If something cannot go on forever, it will stop. If a trend cannot go on forever, there is no need for action or a program to make it stop, much less to make it stop immediately; it will stop of its own accord. Stevens's power law, in psychophysics, relates the intensity of a stimulus to its perceived strength. It supersedes the Weber–Fechner law, since it can describe a wider range of sensations. The theory is named after its inventor, S. Smith Stevens (1906–1973). Stigler's law: No scientific discovery is named after its original discoverer. Named by statistician Stephen Stigler who attributes it to sociologist Robert K. Merton, making the law self-referential. Stokes's law is an expression for the frictional force exerted on spherical objects with very small Reynolds numbers, named for George Gabriel Stokes (1819–1903). Stokes's law of sound attenuation is a formula for the attenuation