John Henry Poynting

POYNTING, JOHN HENRY British physi cist, was born at Monton, near Manchester, on Sept. 9, 1852. He studied at Owens college, Manchester, and at Trinity college, Cambridge. He was bracketed third wrangler in 1876. Poynting went as demonstrator in physics to Owens college, but returned to Cambridge in 1878 on his election as fellow of Trinity col lege. In 188o he was appointed professor of physics at the Mason college, which afterwards became the University of Bir mingham. He retained this post until his death at Birmingham on March 3o, 1914.

Poynting carried out experiments over a period of

12 years to determine the gravitational constant and the mean density of the earth. He used a balance method and during the course of his experiments added considerable knowledge to the technique of accurate weighing. Poynting's best known work is that in the papers "On the Transfer of Energy in the Electromagnetic Field" (Phil. Trans. A., 1884) and "On Electric Currents and the

Electric and Magnetic Induction in the Surrounding Field" (Phil. Trans. A., 1888). In the first paper Poynting showed that the flow of energy at a point could be expressed by a simple formula in terms of the electric and magnetic forces at that point. This is known as Poynting's theorem and the vector is also called by his name. Poynting also wrote papers on radiation and the pres sure of light and several books.

Poynting's interests were very wide; he served as a justice of the peace, was chairman of the Birmingham Horticultural Society and acted as dean of the Faculty of Science. He was elected F.R.S. in 1888.

See his Collected Scientific Papers, edit. by G. A. Shakespear and G. Barlow (192o).