Editing Bolometer (section)

== Langley's bolometer ==

The first bolometers made by Langley consisted of two [[steel]], [[platinum]], or [[palladium]] foil strips covered with [[lampblack]].<ref name="Lang1880">{{cite book |title=The "Bolometer" |author=Langley, S. P. |publisher=American Metrological Society |date=1880-12-23 |page=[https://archive.org/details/bolometerlangley00langrich/page/n6 1]–7 |url=https://archive.org/details/bolometerlangley00langrich}}</ref><ref name="Lang1881">{{cite journal |title=The Bolometer and Radiant Energy |author=Langley, S. P. |journal=Proceedings of the American Academy of Arts and Sciences |volume=16 |date=1881-01-12 |page=348 |doi=10.2307/25138616 |jstor=25138616}}</ref> One strip was shielded from radiation and one exposed to it. The strips formed two branches of a [[Wheatstone bridge]] which was fitted with a sensitive [[galvanometer]] and connected to a battery. Electromagnetic radiation falling on the exposed strip would heat it and change its resistance. By 1880, Langley's bolometer was refined enough to detect thermal radiation from a cow a quarter of a mile (400&nbsp;m) away.<ref>[http://www.hao.ucar.edu/education/bios/langley.php Samuel P. Langley Biography] ({{webarchive|url=https://web.archive.org/web/20091106184818/http://www.hao.ucar.edu/education/bios/langley.php |date=2009-11-06 }}). High Altitude Observatory, University Corporation for Atmospheric Research.</ref> This radiant-heat detector is sensitive to differences in temperature of one hundred-thousandth of a degree Celsius (0.00001&nbsp;°C).<ref>{{Cite web |url=https://earthobservatory.nasa.gov/features/Langley/langley_2.php |title=Samuel Pierpont Langley |date=3 May 2000 |website=earthobservatory.nasa.gov}}</ref> This instrument enabled him to thermally detect across a broad spectrum, noting all the chief [[Fraunhofer line]]s. He also discovered new atomic and molecular absorption lines in the invisible [[infrared]] portion of the electromagnetic spectrum. [[Nikola Tesla]] personally asked Dr.&nbsp;Langley whether he could use his bolometer for his power transmission experiments in 1892. Thanks to that first use, he succeeded in making the first demonstration between West Point and his laboratory on Houston Street.<ref>
{{cite book
 | last1=Tesla
 | first1=Nikola
 | title=NIKOLA TESLA ON HIS WORK WITH ALTERNATING CURRENTS and Their Application to Wireless Telegraphy, Telephony and Transmission of Power : An Extended Interview
 | date=1992
 | publisher=Leland I. Anderson
 | isbn=978-1-893817-01-2
 | chapter-url=http://www.tfcbooks.com/tesla/nt_on_ac.htm#Section_4
 | chapter=section 4
 | quote=I suppose I had hundreds of devices, but the first device that I used, and it was very successful, was an improvement on the bolometer. I met Professor Langley in 1892 at the Royal Institution. He said to me, after I had delivered a lecture, that they were all proud of me. I spoke to him of the bolometer, and remarked that it was a beautiful instrument. I then said, "Professor Langley, I have a suggestion for making an improvement in the bolometer, if you will embody it in the principle." I explained to him how the bolometer could be improved. Professor Langley was very much interested and wrote in his notebook what I suggested. I used what I have termed a small-mass resistance, but of much smaller mass than in the bolometer of Langley, and of much smaller mass than that of any of the devices which have been recorded in patents issued since. Those are clumsy things. I used masses that were not a millionth of the smallest mass described in any of the patents, or in the publications. With such an instrument, I operated, for instance, in West Point—I received signals from my laboratory on Houston Street in West Point.
}}</ref>