In 1876 he published his article On a General Method of describing Plane Curves of the nth degree by Linkwork,[2] which presented a procedure for constructing a linkage that traces an arbitrary algebraic plane curve. This was a remarkable generalization of his work on the design of linkages to trace straight lines. This direct connection between linkages and algebraic curves is now called Kempe's universality theorem.[3] While Kempe's proposed proof was flawed, the first complete proof was provided in 2002, based on his ideas.[4][5]
In 1877 Kempe discovered a new straight line linkage called the Quadruplanar inversor or Sylvester–Kempe Inversor and published his influential lectures on the subject.[6] In 1879 Kempe wrote his famous "proof" of the four colour theorem, shown incorrect by Percy Heawood in 1890. Much later, his work led to fundamental concepts such as the Kempe chain and unavoidable sets.
Kempe (1886) revealed a rather marked philosophical bent, and much influenced Charles Sanders Peirce. Kempe also discovered what are now called multisets, although this fact was not noted until long after his death.[7][8]
Kempe was elected a fellow of the Royal Society in 1881. He was Treasurer and vice-president of the Royal Society 1899–1919. He was a president of the London Mathematical Society from 1892 to 1894. He was also a mountain climber, mostly in Switzerland.
His first wife was Mary, daughter of Sir William Bowman, 1st Baronet; she died in 1893. He then married, in 1897, Ida, daughter of Judge Meadows White, QC. He had two sons and one daughter.