John Tyndall (1820-1893) was an Irish physicist and medical educator. Tyndall's early original work in physics was his experiments on magnetism and diamagnetic polarity, on which he worked from 1850 to 1856. Beginning in the late 1850s, Tyndall studied the action of radiant energy on the constituents of air. He was the first to correctly measure the relative infrared absorptive powers of the gases nitrogen, oxygen, water vapor, carbon dioxide, ozone and methane. He explained the heat in the Earth's atmosphere in terms of the capacities of the various gases in the air to absorb radiant heat (infrared radiation). A very sensitive way to detect particulates is to bathe the air with intense light. The scattering of light by particulate impurities in air and other gases, and in liquids, is known today as the Tyndall Effect or Tyndall Scattering. He was the first to observe and report the phenomenon of thermophoresis in aerosols. He invented a better fireman's respirator, a hood that filtered smoke and noxious gas from air. An index of 19th century scientific research journals has John Tyndall as the author of more than 147 papers, with practically all of them dated between 1850 and 1884, which is an average of more than four papers a year over that 35-year period. Tyndall published seventeen books, which brought state-of-the-art 19th century experimental physics to a wider audience. Besides being a scientist, John Tyndall was a science teacher and evangelist for the cause of science. From 1853 to 1887 he was professor of physics at the Royal Institution of Great Britain in London. In his later years Tyndall often took chloral hydrate to treat his insomnia. In 1893 he died from an accidental overdose of this drug, He was 73 years old.