ATTRACTION. 139 



render this power perceptible. Common electricity is also excited 

 in many ways, but most usually by the friction of glass or resin. 



(6.) Mode of exciting the Voltaic power. Certain combina- 

 tions of metals, usually zinc and copper, with fluids, especially saline 

 and acid fluids, producing opposite polarity at the two extremes 

 of the series. 



(c.) .Mode of receiving and transmitting the power. By conduc- 

 tors, uniting the poles ; they are commonly wires, and are often 

 pointed with well prepared charcoal. 



(d.) Nature of the power. It has been commonly regarded as 

 the same with electricity ; like that it is attended by light, heat, and 

 magnetism, variously modified and combined in different proportions, 

 in different kinds of apparatus ; so that one predominates in one kind 

 and another in another. It is clear that it is not electricity merely. 



(e.) Sensible and demonstrable effects. Attractions and repul- 

 sions, as in common electricity ; similar poles repelling and opposite 

 attracting. All elements and all compound principles, when placed 

 in the electro-galvanic circuit, being for the time endued with polari- 

 ty, chemical decompositions are thus produced. ' Muscular shocks 

 are also among the effects produced by this power, as well as light, 

 heat, and magnetism, which have been already mentioned. 



(/*.) Mode of effecting the decompositions, by bringing the con- 

 necting points into contact with the particular substance. 



(g.) Classification of the elementary bodies. Oxygen, iodine, and 

 chlorine, are attracted to the positive pole, and are therefore said to 

 be electro-negative. 



The combustibles and metals are attracted to the negative pole, 

 and are therefore said to be electro-positive. 



(h.) Classification of the principal proximate principles in the com- 

 pound bodies. The acids go to the positive pole ; the earths, alka- 

 lies and oxides of metals, to the negative. 



(i.) Galvanic electricity is a powerful agent in decomposition ; it 

 is more energetic, and it is also more manageable than common elec- 

 tricity. 



(j.) The arrangement of the principles of bodies under this pow- 

 er, will be mentioned as we come to them individually. 



(k.) The other effects are not material in our present state of ad- 

 vancement ; they will be mentioned in their proper place. 



It is supposed, that the electrical and magnetic attractions are gov- 

 erned by the same general law with gravitation. 



4. COHESION ADHESION AGGREGATION. 



(a.) Cohesion is a union of parts, without change of properties. 

 The particles of a bar of iron cohere ; this force gives the iron 

 its strength ; those of water cohere but feebly ; hence it has no 

 strength ; those of moist dough cohere more than water, &c. These 



