In the year 1736, the French Academy of Sciences proposed, as a subject for a prize, "the Propagation of Heat," when the Marchioness of ChÂtelet entered the list of competitors. Her work was not only an elegant account of all the properties of heat at that time known to natural philosophers, but it was also remarkable for various proposals for experiments; one, among others, which was afterwards followed up by Herschel, and from which he derived one of the chief gems in his brilliant scientific crown.