James Prescott Joule used a falling weight to turn a paddle wheel inside an insulated container of water, converting a precisely known amount of mechanical work into heat and measuring the resulting rise in temperature. Refining the experiment through the 1840s, he published a value of 772.692 foot-pounds of work per British thermal unit in 1850, showing that heat and mechanical energy convert into one another in a fixed, measurable proportion and giving the first law of thermodynamics its experimental foundation.
Facts
YearJoule's refined published value; his first paper on the mechanical equivalent of heat was read in 1845, building on work from 1843. MethodSourced to the subject's own accountJoule used a falling weight of known mass to turn a paddle wheel inside an insulated container of water, converting a precisely measured quantity of mechanical work into heat and measuring the resulting temperature rise. 2 Key FindingSourced to the subject's own accountJoule found a consistent value of 778.24 foot-pound-force of mechanical work per British thermal unit needed to raise a pound of water's temperature by one degree Fahrenheit, giving heat and mechanical energy a fixed, measurable conversion ratio. 2 Cross-Tradition Connections
Sources
1. James Prescott Joule (Britannica)
Encyclopaedia Britannica
2. Mechanical Equivalent of Heat (Wikipedia)
WikipediaHistory and priority dispute sectionQuote, History and priority dispute section
Joule had experimented on the amount of mechanical work generated by friction needed to raise the temperature of a pound of water by one degree Fahrenheit and found a consistent value of 778.24 foot pound force
James Prescott Joule (Wikipedia)
WikipediaWikipedia, James Prescott Joule, Mechanical equivalent of heat sectionQuote, Wikipedia, James Prescott Joule, Mechanical equivalent of heat section
involving the use of a falling weight, in which gravity does the mechanical work, to spin a paddle wheel in an insulated barrel of water which increased the temperature
James Prescott Joule (Wikipedia)
WikipediaWikipedia, James Prescott Joule, 1845 British Association paperQuote, Wikipedia, James Prescott Joule, 1845 British Association paper
He now estimated a mechanical equivalent of 819 foot-pounds force per British thermal unit (4.404 J/cal).
Open Questions (1 open question)
Where did James Prescott Joule perform the mechanical equivalent of heat experiments (paddle-wheel apparatus) that produced his 1850 published value?
Wikipedia's Mechanical equivalent of heat article documents Joule's method and result in detail but names no location. Two candidate sources naming a location (a small laboratory at Pendlebury near Manchester, later moved to his Manchester home after the family brewery was sold) could not be fetched: aps.org returned HTTP 403 and a PMC/NCBI commentary article returned a captcha wall.
What would resolve this A fetchable biography or history-of-science source (not aps.org or PMC/NCBI, both currently blocked) confirming Joule's experimental site by name.
History of ScienceMechanical Equivalent of Heat (Wikipedia)
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