CERAUNICS. 363 



public in 1750. The science of Electro-Magnetism, originated in 

 1820 ; when Oersted of Copenhagen discovered the peculiar action 

 of a galvanic current on a magnetic needle. The initial discovery in 

 Thermo- Electricity, was made by Dr. Seebeck, in 1822. Our his- 

 tory of Meteorology must be so brief that it will be deferred until we 

 come to that science in its place. 



We proceed to speak briefly of Ceraunics ; taking the divisions in 

 the order above named, (p. 361). 



1. The science of Calorics, relates to the phenomena of heat, 

 and the laws of its action. The name is from the Latin, calor, heat : 

 and the name caloric, has been applied to the agent which causes 

 the sensation of heat, and which has long been regarded as a subtile, 

 imponderable fluid, self-repellent, capable of penetrating ponderable 

 substances, and perhaps uniting with them in definite combinations : 

 though recent discoveries strongly favor the extension of the undula- 

 tory theory to heat, as well as to light. The sources of heat, are the 

 sun ; combustion, and other chemical action ; friction, and other 

 mechanical action ; electricity and galvanism ; and animal life. Calo- 

 ric is conceived to exist in two different states ; sensible and latent. 

 Sensible caloric, is that which affects the thermometer, and produces 

 the sensation of heat ; while latent caloric, though supposed to be 

 present in bodies, does not affect the thermometer or the senses; 

 perhaps because it is, as it were, chemically combined with the 

 ponderable substance. 



Caloric is supposed to emanate from all warm bodies, either by 

 radiation or conduction. It is said to be radiated, when it darts forth 

 with great velocity, like light : and it is said to be conducted, when 

 it passes slowly from particle to particle of the surrounding bodies. 

 Caloric radiates best from dark and rough surfaces ; and is best con- 

 ducted by the metals ; more slowly by wood and earths ; and in 

 liquids it is carried upwards chiefly by circulation. Radiated caloric, 

 meeting any substance, is, like light, either reflected, absorbed, or 

 transmitted ; and in the latter case refracted, as in the solar prismatic 

 spectrum. It is best reflected from bright and polished surfaces ; 

 and absorbed by dark and rough ones. The cooling of bodies is, 

 of course, attributed to the abstraction of caloric, from their giving 

 out more than they receive. The effects of caloric, are the expan- 

 sion of nearly all bodies, except melting ice, or antimony, and heated 

 clay ; the liquefaction of solills, and the vaporization of liquids ; in 

 which cases a certain quantity of caloric is supposed to become latent, 

 or chemically combined ; and, finally, the production of light, electri- 

 city, and chemical action. 



2. Electricity, so named from ytextpov, the Greek word for 

 amber, treats of the phenomena first discovered in that substance, 

 when subjected to friction ; and ascribed to an extremely rare or 

 subtile fluid, pervading the material world. If we rub smooth glass 

 with a silken cloth, both substances become electrically excited ; as 

 is proved by their attracting pith balls, or other light bodies near them. 

 This is explained, according to Dr. Franklin's theory, by supposing 

 that the glass becomes charged with an excess of the electric fluid, 

 that is positively excited; and that while this fluid repels its own 



