FLIR PathFindIR User Manual page 34

8 – Infrared Technology
Figure 8-4: Samuel P. Langley (1834–1906)
The improvement of infrared-detector sensitivity progressed slowly.
Another major breakthrough, made by Langley in 1880, was the invention
of the bolometer. This consisted of a thin blackened strip of platinum
connected in one arm of a Wheatstone bridge circuit upon which the
infrared radiation was focused and to which a sensitive galvanometer
responded. This instrument is said to have been able to detect the heat
from a cow at a distance of 400 meters.
An English scientist, Sir James Dewar, first introduced the use of liquefied
gases as cooling agents (such as liquid nitrogen with a temperature of -
196 °C (-320.8 °F)) in low temperature research. In 1892 he invented a
unique vacuum insulating container in which it is possible to store
liquefied gases for entire days. The common 'thermos bottle', used for
storing hot and cold drinks, is based upon his invention.
Between the years 1900 and 1920, the inventors of the world 'discovered'
the infrared. Many patents were issued for devices to detect personnel,
artillery, aircraft, ships—and even icebergs. The first operating systems, in
the modern sense, began to be developed during the 1914–18 war, when
both sides had research programs devoted to the military exploitation of
the infrared. These programs included experimental systems for enemy
intrusion/detection, remote temperature sensing, secure communications,
and 'flying torpedo' guidance. An infrared search system tested during this
period was able to detect an approaching airplane at a distance of 1.5 km
(0.94 miles), or a person more than 300 meters (984 ft.) away.
The most sensitive systems up to this time were all based upon variations
of the bolometer idea, but the period between the two wars saw the
development of two revolutionary new infrared detectors: the image
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