72 CHEMICAL PHYSTCS. 



cntiate it from current electricity, or electricity in motion, which will 

 be considered later. Various machines have been constructed to 

 generate static electricity. In the older forms of such machines 

 friction between glass plates or glass cylinders and pads of silk served 

 as the generating source. In the newer and more powerful forms 

 of static machines, such as the Toepler-Holtz machines, induction 

 chiefly is used to generate the electricity. 



Nature of Electricity. The most modern theory of the nature of elec- 

 tricity teaches that it is a manifestation of some manner of strain set up in the 

 hypothetical ether. But this theory cannot be discussed to advantage in this 

 volume. However, the following lines may assist the student in getting an 

 idea of what electricity is, and how it acts. 



It has been stated that energy is a universal property of matter, and that 

 energy, like matter, can neither be created nor destroyed. But energy, like 

 matter, can be changed from one form .to another, or from one place to 

 another. According to whether energy manifests itself in masses, in mole- 

 cules, or in atoms, we speak of mass energy, molecular energy, and atomic 

 energy. Mass energy becomes manifest in the attractions due to gravitation, 

 such as the fall of bodies; in magnetic attractions, as when a magnet attracts 

 iron ; in electric attractions, as when an electrified body attracts light particles 

 of matter. Molecular energy manifests itself in heat, in light, in magnetism, 

 and in electricity. Just what the difference is between the different kinds of 

 molecular motion that produce in one case heat, in others light or electricity, 

 has never been discovered. It is supposed to be in the form of undulations 

 or vibrations, the heat undulations having one form, the electric undulations 

 another form, so that while both kinds of motion are found in the same body 

 at the same time, they do not interfere with each other. 



Exactly as in the case of heat and light, we have to assume that the propa- 

 gation of electricity through space takes place in the ether. There is, more- 

 over, a mutual reaction between the vibratory motion of the molecules and the 

 undulatory motion of the ether, the vibrations producing the undulations, and 

 the undulations, in turn, producing the vibrations; just as the vibratory strokes 

 of an oar produce waves, which in turn may produce vibrations in other oars 

 resting in the water. 



The conclusion, therefore, to which we come in regard to the nature of elec- 

 tricity is this : Electricity is a manifestation of energy believed to consist in 

 undulations of the ether and vibrations of the grosser molecules of matter. 



We see, then, that electricity is neither energy nor matter, but, like heat, 

 light, and sound, it is an effect produced by energy on matter. But as the 

 effect cannot be separated from its cause, it is convenient to speak of it as 

 electric energy, in the same sense as we speak of mechanical enegy, vital energy, 

 heat energy, or energy in any other form in which it becomes manifest as asso- 

 ciated with matter. 



To obtain electricity, energy in some other form must be expended, whether 

 it be the energy of our body expended in rubbing together pieces of glass and 

 silk, or the energy of chemical action, as in a battery cell, or the potential 



