Sir Richard Threlfall (14 August 1861 – 10 July 1932)[1] was an English chemist and engineer, he established the School of Physics at the University of Sydney and made important contributions to military science during World War I.

After the discovery new waves by Heinrich Hertz, Threlfall suggested in a 1890 oral discussion that "Signaling, for instance, might be accomplished secretly by means of a sort of electric ray flasher", thus predicting yet-uninvented radio communications.

He obtained leave of absence in 1898 to inquire into methods of teaching electrical subjects in Europe, but on his return resigned his chair as from 31 December 1898, as circumstances had made it necessary that he should live in England.

His experience in this direction was to prove of the greatest service to his country during the 1914–18 war, particularly in connexion with smoke screens and tracer bullets.

Originally designed as an incendiary device to destroy long grass in front of the trenches that gave cover to enemy raiding parties, it also had a useful smoke-producing effect and was used at the Battle of Loos.

Though his main work was in industrial chemistry he kept up his interest in pure science, and was a frequent attendant at meetings of the Royal Society of London.