FLIR FlashSight User Manual page 21

FlashSight™ User's Guide
made the image visible to the eye. Sir John also managed to obtain a
primitive record of the thermal image on paper, which he called a
'thermograph'.
Figure 18: 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 converter
and the photon detector. At first, the image converter received the greatest
attention by the military, because it enabled an observer for the first time in
history to literally 'see in the dark'. However, the sensitivity of the image
converter was limited to the near infrared wavelengths, and the most
interesting military targets (i.e. enemy soldiers) had to be illuminated by
infrared search beams. Since this involved the risk of giving away the
observer's position to a similarly-equipped enemy observer, it is
understandable that military interest in the image converter eventually faded.
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