relates the frequency of modes of vibration for flat circular surfaces with fixed center as a function of the numbers of diametric (linear) nodes and of radial (circular) nodes. Named after Ernst Chladni. Claasen's law, or the logarithmic law of usefulness: usefulness = log(technology). Clarke's three laws, formulated by Arthur C. Clarke. Several corollaries to these laws have also been proposed. First law: When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong. Second law: The only way of discovering the limits of the possible is to venture a little way past them into the impossible. Third law: Any sufficiently advanced technology is indistinguishable from magic. Conway's law: Any piece of software reflects the organizational structure that produced it. Named after Melvin Conway. Cooper's law: The number of radio frequency conversations which can be concurrently conducted in a given area doubles every 30 months. Cope's rule: Population lineages tend to increase in body size over evolutionary time. Coulomb's law is an inverse-square law indicating the magnitude and direction of electrostatic force that one stationary, electrically charged object of small dimensions (ideally, a point source) exerts on another. It is named after Charles-Augustin de Coulomb. Cramer's rule: In linear algebra, an explicit formula for the solution of a system of linear equations with as many equations as unknowns, valid whenever the system has a unique solution. Named after Swiss mathematician Gabriel Cramer. Cromwell's rule states that the use of prior probabilities of 0 ("the event will definitely not occur") or 1 ("the event will definitely occur") should be avoided, except when applied to statements that are logically true or false, such as 2+2 equaling 4 or 5. Cunningham's law: The best way to get the right answer on the Internet is not to ask a question, but to post the wrong answer. Attributed to Ward Cunningham by Steven McGeady. Curie's law: In a paramagnetic material the magnetization of the material is (approximately) directly proportional to an applied magnetic field. Named after Pierre Curie. Curie-Weiss law: describes the magnetic susceptibility χ of a ferromagnet in the paramagnetic region above the Curie point. Named after Pierre Curie and Pierre-Ernest Weiss. D'Alembert's principle: The sum of the differences between the forces acting on a system of mass particles and the time derivatives of the momenta of