in repeating and extending these experiments, being satisfied that the grand agents of nature are, by the Creator's fiat, _indestructible_, and that wherever mechanical force is expended, an exact equivalent of heat is always obtained."
This was the first determination of the dynamical equivalent of heat. Other naturalists and experimenters about the same time were attempting to compare the quantity of heat produced under certain circumstances with the quantity of work expended in producing it; and results and deductions (some of them very remarkable) were given by Séguin (1839), Mayer (1842), Colding (1843), founded partly on experiment, and partly on a kind of metaphysical reasoning. It was Joule, however, who first definitely proposed the problem of determining the relation between heat produced and work done in any mechanical action, and solved the problem directly.
It is not to be supposed that Joule's discovery and the results of his investigation met with immediate attention or with read