Sir William Henry Preece KCB FRS (15 February 1834 – 6 November 1913) was a Welsh electrical engineer and inventor.

Upon his retirement from the Post Office in 1899, Preece was made a Knight Commander of the Order of the Bath (KCB) in the 1899 Birthday Honours.

Upon Lodge's proposal of "loading coils" applied to submerged cables, Preece did not realise that "Earthing" would extend the distance and efficiency.

Preece believed incorrectly that the Earth's magnetic field was critical in the propagation of radio waves over long distances.

It was derisively referred to as "the drain-pipe theory" by Heaviside, because Preece relied on an analogy between electricity and water for thought experiments.

[5] Preece once stated, conveying sentiments later expressed by Edwin Armstrong, True theory does not require the abstruse language of mathematics to make it clear and to render it acceptable [...] All that is solid and substantial in science and usefully applied in practice, have been made clear by relegating mathematic symbols to their proper store place – the study.Preece served as president of the Institution of Civil Engineers between April 1898 and November 1899.