1616-1703

English mathematician who, with Christiaan Huygens and Christopher Wren, established conservation of momentum (1668). In Arithmetica Infinitorum (1656) he presented a method for calculating areas under curves using infinite sums, which greatly influenced Isaac Newton's development of calculus. Wallis extended exponents to negative numbers and fractions, first used ∞ to symbolize infinity, represented imaginary numbers geometrically, and produced an infinite product for π. He also wrote on grammar, logic, and theology; was an expert on decipherment; and taught deaf-mutes to speak.