On the dynamical theory of heat, with numerical results deduced from Mr Joule's equivalent of a thermal unit, and M. Regnault's Observations on steam.

From: Transactions of the Royal Society of Edinburgh, Volume 20 (1853), Pages 261-288. Article by William Thomson (later Lord Kelvin). Pts. 1-3 of a series of papers by Kelvin on this topic.
Paper was read to the Royal Society of Edinburgh on 17th March 1851.