570. _Why is "positive" electricity called also "vitreous," and "negative" electricity called also "resinous"?_ Because some philosophers believe that there is but _one electricity_, but that it is liable to variations of _quantity_ or _state_, which they distinguish by _positive_ and _negative_; while other philosophers believe that there are _two electricities_, which they name _vitreous_ and _resinous_, because they may be induced respectively from _vitreous_ and _resinous_ substances, and they display forces of attraction and repulsion. 571. _Upon what do the electrical phenomena of nature depend?_ Upon the tendency of _electricity_ to find an _equilibrium_ between its _positive_ and _negative_ states (assuming there to be but _one_ fluid); or upon the tendency of _vitreous electricity_ to seek out and combine with _resinous electricity_ (assuming that there are _two_ fluids). [Verse: "The Lord also thundered in the heavens, and the Highest gave his voice; hailstones and coals of fire."] 572. _How does the equilibrium of electricity become disturbed?_ By changes in the condition of matter. As electricity resides in all substances, and is, perhaps, an essential ingredient in their condition, so every change in the state of matter--whether from heat to cold, or from cold to heat; from a state of rest to that of motion; from the solid to the liquid, or the æriform condition, or _vice versa_; or whether substances combine chemically and produce new compounds--in every change _the electrical equilibrium is disturbed_; and, in proportion to the degree of disturbance, is the force exerted by electricity to resume its balance in the scale of nature. 573. _How does electricity seek to regain equilibrium?_ By passing through substances that are favourable to its diffusion; therefore they are called _conducting_ or _non-conducting_ bodies, according as they favour or oppose the transmission of the electrical current. 574. _What substances are conductors of electricity?_ Metals, charcoal, animal fluids, water, vegetable bodies, animal bodies, flame, smoke, vapour, &c. 575. _What substances are non-conductors?_ Rust, oils, phosphorous, lime, chalk, caoutchouc, gutta percha, camphor, marble, porcelain, dry gases and air, feathers, hair, wool, silk, glass, transparent stones, vitrefactions, wax, amber, &c. These bodies are also called _insulators_. Some of these substances, as chalk, feathers, hair, wool, silk, &c., though non-conductors when _dry_, become conductors when _wetted_. _Insulating_--preventing from escaping. 576. _Why are amber and wax classed among the non-conductors, when they have been pointed out as electrics, and used to illustrate electrical force?_