Tyndall's Experiments
In 1859, aged 39, Tyndall began investigating radiant heat and the acoustic
properties of the atmosphere. Part of his experimentation included the
construction of the first ratio spectrophotometer which he used to measure the
absorptive powers of gases such as water vapour, carbonic acid,
ozone and hydrocarbons. Amongst his most important discoveries were the vast
differences in the abilities of "…perfectly colourless and invisible
gases and vapours…" to absorb and transmit radiant heat. He noted that
oxygen, nitrogen and hydrogen are almost transparent to radiant heat, whilst
other gases are quite opaque.
Tyndall showed that ozone was an oxygen cluster rather than a hydrogen compound.
He was the inventor of the firemans respirator and made other less well-known
inventions including better fog-horns. One of his most important inventions, the
light pipe, has led to the development of fibre optics. The modern light
instrument is known as the gastroscope, which enables internal observations of a
patient's stomach without surgery.
Tyndall's experiments also showed that molecules of water vapour, carbon dioxide
and ozone are the best absorbers of heat radiation and that even in small
quantities these gases absorb much more strongly than the atmosphere itself, a
phenomenon of great meteorological importance. He concluded that among the
constituents of the atmosphere, water vapour is the strongest absorber of
radiant heat and is therefore the most important gas controlling the Earth's
surface air temperature. He said that without water vapour the Earth's surface
would be "held fast in the iron grip of frost". He later speculated
how changes in water vapour and carbon dioxide could be related to climate
change.
In
the course of his study into light beams he discovered in 1869 the Tyndall
effect - the diffusion of light by large molecules and dust. His suggestion that
the sky's blue is due to the scattering of the suns rays by molecules in the
atmosphere, a phenomenon that was later explained theoretically by Lord Rayleigh. The bluish plane polarised light scattered in the Tyndall effect is
called Tyndall blue and the luminous path formed in the Tyndall effect by the
breaking up of the entering light by suspended particles is known as a Tyndall
cone. He is credited with the first ever atmospheric pollution measurements
using infrared and scattering measurement instruments to monitor the London
atmosphere.