Analyse This Th Is Apparatus, Held in London’S Science Museum, Has Some Signifi Cant Purpose — Or Curiosity Value — in the History of Physics

ENDGAME Analyse this Th is apparatus, held in London’s Science Museum, has some signifi cant purpose — or curiosity value — in the history of physics. Can you guess what it is?

IT “WEAVES ALGEBRAIC PATTERNS JUST AS THE JACQUARD LOOM WEAVES FLOWERS AND LEAVES”. ANSWER NEXT MONTH.

James Prescott Joule was the In 1845, Joule performed his by”. It was only through using son of a wealthy brewer in fi rst paddle-wheel experiment, very sensitive thermometers, Manchester, in the north of churning the water in a constructed especially for this England. He received his early calorimeter using paddles driven experiment, that Joule was able to scientifi c education from by falling weights. Aft er a series reach a consistent result. another well-known Mancunian, of painstaking experiments The paddle-wheel John Dalton. Joule began to using sperm oil and mercury experiments became classics investigate the fast-developing as well as water, he reached the in the history of science. The topic of electricity generation conclusion that a weight of 772 rotating vanes pass through the in the 1830s, wanting to make pounds (350 kg) falling through gaps between a set of fixed vanes comparisons between the a distance of 1 foot (0.3 m) raises to cause maximum resistance effi ciency of various energy the temperature of 1 pound to the water or other liquid. It sources. In the 1840s he became (0.45 kg) of water by 1 degree is not so much the result that is interested in heat, which was Fahrenheit. He called this the remembered now, but the fact then seen as a wasteful by- Last month: ‘mechanical equivalent of heat’. that Joule had shown that heat product of useful work. By 1843 Joule’s paddle wheel His results were not had a mechanical equivalent. he was convinced that “wherever universally accepted because the mechanical force is expended, an observational eff ects were small. JANE WESS exact equivalent of heat is always William Th omson, later Lord Jane Wess is a curator at the expended”. He began a series of Kelvin, recorded that a Fellow of Science Museum, Exhibition experiments comparing the work the Royal Society objected because Road, South Kensington, London done in various forms with the “he had nothing but hundredths SW7 2DD, UK. resulting heat produced. of a degree to prove his case www.sciencemuseum.org.uk

132 nature physics | VOL 2 | FEBRUARY 2006 | www.nature.com/naturephysics