I. New determination of the mechanical equivalent of heat

An account is given by the author, of the experiments he has recently made, with a view to increase the accuracy of the results given in his former paper, published in the “Philosophical Transactions” for 1850. The result he has now arrived at, from the thermal effects of the friction of water, is, that taking the unit of heat as that which can raise a pound of water, weighed in vacuo, from 60° to 61° of the mercurial thermometer; its mechanical equivalent, reduced to the sea-level at the latitude of Greenwich, is 772·55 foot-pounds.