Jan Ingenhousz

Physician and plant physiologist, born in Breda, S Netherlands. He practised as a doctor in England, then became physician to Empress Maria Theresa. He improved methods of generating static electricity (1766), and was the first to make quantitative measurements of heat conduction in metals. He is best known as the discoverer of photosynthesis (1779).

Jan Ingenhousz or Ingen-Housz (December 8, 1730 - September 7, 1799) was a Dutch-born British physiologist, botanist and physicist.

Ingenhousz discovered that, in the presence of light, plants give off bubbles from their green parts while, in the shade, the bubbles eventually stop. He also discovered that, in the dark, plants give off carbon dioxide. He realised as well that the amount of oxygen given off in the light is more than the amount of carbon dioxide given off in the dark.

In 1785, he described the irregular movement of carbon dust on alcohol and therefore has a claim as discoverer of what came to be known as brownian motion.