Henry Letheby (1816 – 28 March 1876) was an English analytical chemist and public health officer.
Letheby was born at Plymouth, England, in 1816, and studied chemistry at the Royal Cornwall Polytechnic Society.
Letheby was an extremely accurate technological chemist and contributed many papers to The Lancet and other scientific periodicals.
Letheby's chief work was the treatise On Food, Its Varieties, Chemical Composition, Nutriitive Value, Comparative Digestibility, Physiological Functions and Uses, Preparation, Culinary Treatment, Preservation, Adulteration &c., London, 1870.
Letheby's design caused only either the make or the break current to flow to the patient by a mechanical arrangement of two spoked wheels.