John Henry Poynting, English physicist, early 20th century.
© Science Museum / Science & Society Picture Library
John Henry Poynting (1852-1914) demonstrated the existence of radiation presure and was President of the Physical Society from 1905-6. Poynting's 1884 paper 'On the Transfer of Energy in the Electromagnetic Field' contained his formula for connecting mechanical motion with electromagnetic forces. Poynting also showed that radiation has momentum, exerting a large presure under astronomical conditions.