CHEMISTRY. 37 



differ in their properties: those proceeding from red hot 

 copper and fluor spar, differ from those from an oil lamp or 

 the sun. Cold is merely a negative condition depending on 

 the absence of heat. 



There are several sources of caloric, of which the sun is the 

 principal, and compared with which all others are insignificant. 

 The sun radiates heating as well as luminous rays, which 

 reach the earth, and are partly absorbed and partly reflected. 

 The combustion of bodies is another source, electricity, gal- 

 vanism, friction, condensation, animal vital action, and chemical 

 action, are all sources of caloric. The earth is supposed to 

 contain in its interior a vast amount of heat. The relations 

 of heat to the growth of vegetation are important, and will be 

 noticed in another place. 



ELECTRICITY. 



Electricity is a fluid or principle pervading all nature, so far 

 as we kno\v. The first full investigation of this extensive and 

 interesting branch of science was made by Dr. Franklin ; and 

 although it is only a few years since, yet it has become iden- 

 tified with almost every branch of physical science, and has 

 already had an immense influence on the moral and social, 

 as well as commercial condition of the civilized world. We 

 still know little of the nature of electricity ; although many of 

 its properties and effects are somewhat well understood, still 

 all investigation and discovery has only tended to render its 

 true nature and phenomena more mysterious, and its origin 

 more questionable. We see its effects, but what it is, or 

 whence it originates, we know not 



But for the sake of convenience, philosophers have applied 

 certain terms to its peculiar properties : these terms in some 

 cases indicate particular effects and conditions, and in others 

 they may be said to be little more than names for our 

 ignorance. Electricity is supposed to be a fluid which exists 



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