Heat, signifies either the pe-culiar sensation we feel on the approach of burning bodies, or the cause of that effect, which is Fire.
Heat is now universally considered as a modification of a fluid; but, after the various inquiries of the most able chemists, much remains to be done towards ascertaining all the phenomena of this subtle and invisible element. In this place, we shall only select a few principles' in some degree illustrative of its nature and properties : 1. Heat and cold mutually expel each other. 2. Heat is visibly occasioned by the concentration of the rays of the sun, and also of the electric fluid. As fire, therefore, is evidently the cause of heat, it follows that both the light of the sun and the electric fluid are elementary fire. 3. Heat expands bodies in every direction ; hence the elementary fluid, when producing heat, acts from a centre towards a circumference; and, when it generates cold, moves In a contrary direction. 4. It. is, therefore, impossible to calculate the precise quantity of heat which any substance contains. 5. Heat assists the progress of vegetation, but too intense a degree of it produces effects totally different. 6. When latent heat is transferred to external bodies, vapours become condensed, and in some cases return to their original state: in others, they are productive of light, and a vehement degree of sensible heat, whence the different phenomena of Distillation, Evaporation-, etc.