26 ELEMENTS OF STATIC ELECTRICITY. 



made to do by a system of ropes and pulleys. The 

 20 foot-pounds of energy expended must exactly 

 equal the 20 foot-pounds stored up; and the height 

 through which the large weight is raised is to that 

 through which the small weight descends in the in- 

 verse ratio of the mass of each. 



In all electric work, of whatever nature, the same 

 principle will be found to hold true ; gravity potential 

 in this case representing electric potential in electric 

 work. Mechanical work may re-appear as electric work, 

 or electric as mechanical work; the energy produced 

 being always, in some form, equal to the energy 

 expended. 



PIEAT, LIGHT, AND ELECTRICITY COMPARED. The 

 weight of evidence goes to show that electricity, like 

 heat and light, belongs to that kind of energy known 

 as molecular ; and whatever is known as to one kind of 

 energy may, by analogy, be inferred as to other kinds 

 of the same class, with such modifications as distin- 

 guish different species of the same genus. 



There is ample proof that heat is a mode of molec- 

 ular motion. Not that the heat produces the motion, or 

 the motion the heat, but that it is motion ; that the 

 molecules of matter being thrown into a certain kind 

 of motion, the result is the sensation known as heat. 



According to the universally accepted theory of 

 light, it is another species of motion of the same 

 kind ; and there are indications that light and elec- 

 tricity are identical. But, if not identical, we may 

 at least assume that they are closely allied to each 

 other. 



We find also that the same causes, acting at the 

 same time, on the same bodies, and under the same 



