since the enunciation of atomic doctrines by the old Greek philosophers—and from their great suggestiveness—the speculations of reflective minds have wandered over wellnigh every imaginable hypothesis, and approximated with greater or less minuteness to the views which are admitted now, and which we think to be supported by experiment. Thus, as a case in point, we may refer to Galileo,[1] whose resource of observation could have scarcely been superior to Archimedes's, and who would seem to have conceived of an increase of heat as only a more elementary condition of material substance, in which the more or less considerable destruction of molecular bonds allowed the individual particles of a body to move among themselves with a more unconstrained vibration.
But very few among the countless suppositions which we might thus succeed in raking up, however curious or predictive in themselves, would have the slightest bearing on our present subject. Developed only to the extent demanded by the superiority of the scholastic mind, they would be found in general mere arbitrary, whimsical assertions; untried and unsupported by critically-devised experiments. With the reformation of philosophy does our historical sketch then properly begin, and, moreover, with Lord Bacon as its founder; for, in illustrating the proper method of establishing a philosophical doctrine, he forever identified himself with the dynamic theory, by showing that the most comprehensive explanations were afforded by considering heat to be an intestine motion of the constituent particles of a body. Systematically reviewing the known properties and effects of heat—the only practicable course open to him—he concluded in the following memorable and oft-quoted passages:[2]
We find, therefore, in older writings, the first considerable support of this doctrine attributed to Bacon; and it must be conceded that to the power and vividness with which he portrayed his conception of this agent was due in a great measure the tenacity with which it was afterward, from time to time, brought forward and upheld.
The subsequent supporters of this view, though not perhaps most numerous, comprised by far the most distinguished and profound philosophers of their time, their writings furnishing many remarkable anticipations of heat-theory as now received.
