Family of Swiss mathematicians. Jacques (or Jakob) (1654-1705) was a major developer of calculus and made an important contribution to probability theory. His brother Jean (or Johann) (1667-1748) also developed calculus and contributed to the study of complex numbers and trigonometry. Jean's son Daniel (1700-1782) pioneered the modern field of hydrodynamics and anticipated the kinetic theory of gases, indicating that gas pressure would increase with increasing energy. He was also one of the first scientists to understand the concept of conservation of energy.