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at the lower end. The scale was divided into 240 equidistant parts. The unheated piece of clay would fit the 0.5-inch gap giving the zero temperature reading. After annealing, the clay cylinder would shrink and fit somewhere in between the left and right ends of the bars, and the temperature could be read from the scales on the bars.
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To facilitate the temperature calculation, Wedgwood built a device which would directly read the temperature. Two metal bars with scales on them were fixed one above another on a metal plate and inclined at a small angle. The spacing between the bars was 0.5 inches at one end and 0.3 inches
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used his pyrometer to evaluate the temperature scale of
Wedgwood and came to the conclusion that the starting point should be significantly lower, at 517 °F (269 °C) instead of 1,077.5 °F (580.8 °C), and that the steps should be nearly halved from 130 °F (72 °C) to no
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The origin on the
Wedgwood scale (0 °W) was set at the onset temperature of red heat, 1,077.5 °F (580.8 °C). The scale had 240 steps of 130 °F (72 °C) and extended up to 32,277 °F (17,914 °C). Wedgwood tried to compare his scale with other scales by measuring the
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A 0.5-inch-diameter cylinder made from pipe clay was dried at the temperature of boiling water. This would prepare it for heating in the oven in which the temperature was to be measured. During the annealing, sintering (merging) of fine particles resulted in contraction of clay. After cooling, the
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To solve this problem, in 1782, Wedgwood created an accurately scaled pyrometric device, with details published in the
Philosophical Transactions of the Royal Society of London in 1782 (Vol. LXXII, part 2). This led him to be elected a fellow of the
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Natural
Philosophy. Volume 2. Popular Introductions to Natural Philosophy. Newton's Optics. Description of Optical Instruments. Thermometer and Pyrometer. With an Explanation of Scientific Terms, and an
76:. The scale started at 1,077.5 °F (580.8 °C) being 0 °W and had 240 steps of 130 °F (72 °C). Both the origin and the step were later found inaccurate.
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more than 62.5 °F (34.7 °C). However, even after this revision the
Wedgwood measurements overestimated the melting points of elements.
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temperature was evaluated from the diameter difference before and after heating assuming that the contraction is linear with temperature.
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to temperatures below 356 °C, which is too low for many industrial applications such as pottery, glass making and metallurgy.
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A dictionary of science, literature and art, ed. By W.T. Brande assisted by J. Cauvin. Ed. By W.T. Brande and G.W. Cox.3 vols
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142:(32 °W or 5,237 °F (2,892 °C)). All these values are at least 2,500 °F (1,400 °C) too high.
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72:, and the shrinking was evaluated by comparing heated and unheated clay cylinders. It was the first standardised
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of mercury of 356 °C (673 °F). The scale and associated measurement technique were proposed by the
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Johann Samuel
Traugott Gehler's physikalisches Wörterbuch: Bd., 1. Abth. (1833) N-Pn; 2. Abth. (1834) Po-R
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239:"Philosophical Transactions of the Royal Society of London. Vol. LXXII. For the Year 1782. Part II"
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A device for converting the diameter of the annealed clay cylinder into the
Wedgwood temperature.
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The world in a crucible: laboratory practice and geological theory at the beginning of geology
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as a function of temperature. He also determined the melting points of three metals, namely
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183:"Wedgwood Pyrometer by J. Newman, 1827-56 | Science Museum Group Collection"
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211:"Image of wedgwood pyrometer, 1786. By Science & Society Picture Library"
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312:"BBC – History – Historic Figures: Josiah Wedgwood (1730–1795)"
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Gehler, Johann Samuel
Traugott; Littrow, Karl Ludwig (1834).
272:"Presidential Address: Josiah Wedgwood (1730–95): Scientist"
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in the 18th century. The measurement was based on the
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50:, which was used to measure temperatures above the
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134:(27 °W or 4,587 °F (2,531 °C)),
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276:The British Journal for the History of Science
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84:The boiling point of mercury limits the
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197:"Museo Galileo - Wedgwood pyrometer"
164:Outline of metrology and measurement
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24:
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602:Science and technology in England
423:. Geological Society of America.
349:Justus Liebig (Freiherr) (1854).
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151:Louis-Bernard Guyton de Morveau
355:(in German). pp. 713–714.
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592:Obsolete units of measurement
417:Newcomb, Sally (2009-02-15).
402:. E. B. Schurckert. p.
86:mercury-in-glass thermometer
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270:Chaldecott, J. A. (1975).
243:The London Medical Journal
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68:of clay when heated above
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289:10.1017/s0007087400013674
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375:. 1832. pp. 27–30.
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225:"Wedgwood's pyrometer"
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597:Scales of temperature
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249:(3): 225–235. 1783.
170:Notes and references
547:Conversion formulas
338:. pp. 149–150.
332:Dictionary (1867).
27:Unit of temperature
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430:978-0-8137-2449-2
382:978-0-543-88106-9
74:pyrometric device
48:temperature scale
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18:Degree Wedgwood
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40:Wedgwood scale
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475:temperature
282:(1): 1–16.
146:Corrections
586:Categories
551:comparison
496:Fahrenheit
316:bbc.co.uk
66:shrinking
536:Wedgwood
501:Gas mark
158:See also
70:red heat
526:Réaumur
521:Rankine
491:Delisle
486:Celsius
298:4025813
256:5545481
80:History
56:English
576:Energy
562:Portal
516:Newton
511:Leiden
506:Kelvin
471:Scales
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136:silver
132:copper
128:silver
100:Method
59:potter
531:Rømer
372:Index
294:JSTOR
121:Scale
549:and
425:ISBN
377:ISBN
140:gold
38:The
473:of
404:986
284:doi
251:PMC
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44:°W
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