Joule Paddle Wheel

1845 · Falling Weight Apparatus · Work 232 of 1,871

Joule Paddle Wheel, 1845, Falling Weight Apparatus

Joule's paddle wheel apparatus in a Manchester cellar, a brass calorimeter can with vanes inside driven by cords over pulleys from two falling weights, thermometer in the lid.

What it was used for
James Prescott Joule, manager of the family brewery from 1837 and self-taught, drove a paddle wheel in a vessel of water by falling weights. Friction warmed the water by about one degree Celsius; from the work of the falling weights and the temperature rise he calculated how much work equals a given quantity of heat. By his own account, the paddle wheel gave 781.5 (water), 782.1 (sperm oil) and 787.6 (mercury) foot-pounds in 1845 and 1847. His final value in the Philosophical Transactions of 1850: 772 foot-pounds raise one pound of water by one degree Fahrenheit. The paddle wheel at the Science and Industry Museum, Manchester, is dated c.1860.
What was new
What was new was not the idea that friction makes heat (Rumford, boring cannon) but a number: with water, oil, mercury, an electromagnetic machine and gases Joule kept getting roughly the same conversion value. In 1843 he had still given 838 foot-pounds. This required, by his own claim, measuring temperatures to 1/200 of a degree Fahrenheit. The twist: in 1843 he is said to have met stony silence at the British Association and in 1844 the Royal Society declined his work; in 1847 at Oxford he met William Thomson, who became his collaborator, and in 1850 Joule was elected a Fellow of that same Royal Society.

Further reading