The susceptibility (X) of a paramagnetic substance is proportional to the thermodynamic temperature (T), i.e. x = C/T, where C is the Curie constant. A modification of this law, the Curie-Weiss law, is more generally applicable. It states that X = C/(T- θ), where θ is the Weiss constant, a characteristic of the material. The law was first proposed by Pierre Curie and modified by another French physicist, Pierre-Ernest Weiss (1865-1940).