Mechanical equivalent of heat
Equivalente mecánico del calor
- Date
- 1843-1849 · confidence high
- Place
- Manchester (Salford), England, United Kingdom
- Credited to
- James Prescott Joule; Julius Robert von Mayer
- People
- 👤 James Prescott Joule1818–1889👤 Julius von Mayer1814–1878
- Field
- Matter & energy
⚠️ Disputed: the sources disagree.
What was discovered
Joule measures, by stirring water with paddles, that a fixed amount of work always produces the same amount of heat (about 4.18 J per calorie). Heat is not a substance but a form of energy interchangeable with work.
Mayer published in 1842 (Heilbronn) the theoretical value from the specific heats of gases, but was ignored; a bitter priority dispute with Joule followed.
What it led to
- Conservation of energy
- First law of thermodynamics
- End of the caloric theory
- Kinetic theory of heat
Built on
- Rumford's cannon-boring experiments (1798)
- Black's calorimetry
- Electric motors and batteries (Joule effect, 1841)
Made possible
- Conservation of energy1847
- First law of thermodynamics1850
- Precision calorimeters
- Unit of energy (joule)