Burning Mirror

Burning Mirror

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Joseph Priestley (1733–1804) used this reflector in his Northumberland, Pennsylvania laboratory. Priestley, the noted chemist whose accomplishments include the discovery of oxygen, was born in England. He lived and worked in Birmingham for many years, but his views as a Dissenter and an advocate of the French Revolution incited an angry mob into burning down his house and laboratory. In 1794 he fled to America, eventually settling in Northumberland, near Philadelphia. His great-great-granddaughter, Frances Priestley, donated his surviving laboratory ware to the Smithsonian in 1883.
To study the gas given off from a burning material, Priestley required a way to heat or ignite a sample while it was enclosed in a glass vessel, thus trapping the emitted gas for study. His preference seems to have been to use a burning glass (see object CH*319022) to focus sunlight into a hot beam. However, sunlight could not always be relied upon, particularly in England’s dreary weather. On an overcast day, he would have needed an alternate way to generate focused heat, and likely would have relied on this reflector. A pair of these reflectors, raised to the same height and separated by a distance of about ten to fifteen feet, could be used, with the help of a heat source, to ignite a sample. The heat source (say a red hot ball of iron on a stand) would be placed in the focus of one reflector and the sample to be ignited placed in the focus of the second reflector. Heat from the iron would reflect off of the first reflector and onto the second, from which it was next reflected onto the sample. A mid-20th century catalogue of scientific instruments describes the heat generated by this set-up as sufficient to ignite phosphorous.
This set-up, however, does not seem to be explicitly mentioned by Priestley. Rather than a pair of burning mirrors, he tends to refer to a single mirror. He notes the drawback of the mirror in Experiments and observations on different kinds of air, Vol. II: “... the nature of this instrument is such, that it cannot be applied, with effect, except upon substances that are capable of being suspended, or resting on a very slender support. It cannot be directed at all upon any substance in the form of powder, nor hardly upon anything that requires to be put into a vessel of quicksilver; which appears to me to be the most accurate method of extracting air from a great variety of substances.”
Badash, Lawrence. “Joseph Priestley’s Apparatus for Pneumatic Chemistry.” Journal of the History of Medicine and Allied Sciences 19, no. 2 (1964): 139–55. doi:10.1093/jhmas/XIX.2.139.
Benjamin Pike. Pike’s Illustrated Descriptive Catalogue of Optical, Mathematical and Philosophical Instruments: Manufactured, Imported, and Sold by the Author; with the Prices Affixed at Which They Are Offered in 1848... The author.
National Museum of American History Accession File #13305
National Museum of American History Accession File #229395
Priestley, Joseph. Experiments and Observations on Different Kinds of Air. 2d ed., 1775. cor.... London,. http://hdl.handle.net/2027/nyp.33433079424671.
———. 1781. Experiments and Observations on Different Kinds of Air... /. The third edition corrected. London : http://hdl.handle.net/2027/ucm.532738264x.
Priestley, Joseph, and John Towill Rutt. 1817. The Theological and Miscellaneous Works of Joseph Priestley. Vol. I Part 2. [London : Printed by G. Smallfield. http://archive.org/details/theologicalmisce0102prie.
Currently not on view
Object Name
burning mirror
used by
Priestley, Joseph
Associated Place
United States: New Jersey
Physical Description
brass (overall material)
wood (overall material)
overall: 17 in x 12 1/2 in; 43.18 cm x 31.75 cm
ID Number
catalog number
accession number
Credit Line
Gift of Miss Frances D. Priestley
Science & Scientific Instruments
See more items in
Medicine and Science: Chemistry
Science & Mathematics
Joseph Priestley
Data Source
National Museum of American History
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did priestly used a burning mirror to light the candle which is inside the bell jar without disturbing the setup from outside?

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