The substances are disposed in the order of their perfection; that is, the best conductors and the best electrics are placed at the head of their respective lists, and those of an inferior kind follow, somewhat in the manner of a scale graduated downward. Perfect exactness however is not to be here expected, because the subject forbids it, and some of the specified articles are of classes of substances among which there may be a sensible difference. _Conductors or non-electrics._ Gold, Silver, Copper, Platina, Brass, Iron, Tin, Mercury, Lead, Semi-metals. Metallic ores.—Of which those are the best which contain the greatest number of metallic parts and are nearest to a reguline state. Charcoal, either of animal or vegetable substances— Animal fluids, Acids, Saline substances, Hot water, Cold water, Salt water, All other liquids except oils, Red hot glass, Melted rosin, Flame and the effluvia of flaming bodies,[10] Ice and snow—but not below the temperature of 13° Fahrenheit. Earthy and stony substances, of which the hardest are the worst. Glass filled with boiling water, Vapour or steam of boiling water, Smoke. All compounds which contain the above substances in different proportions, are conductors in different degrees. _Non-conductors or electrics._ Glass and all vitrifications; even those of metals. All gems, of which the most transparent are generally the best. All resinous substances and resinous compounds, Amber, Sulphur, Baked wood—if not suffered to imbibe moisture. All bituminous substances, Wax, Silk, Cotton. All dry animal excrescences; as feathers, hair, wool, horn, &c. Paper, White sugar and sugar candy, Atmospheric air and other gasses, Oils, Dry and complete metallic oxyds, The ashes of animal and vegetable substances, All hard stones; of which the hardest are the best, Powders not metallic. Ice at and below the temperature of 13° of Fahrenheit’s thermometer. According to Mr. Walsh’s and Mr. Morgan’s experiments, the Torricellian vacuum ought to be placed at the head of this list; but the singular nature of a vacuum, though a non-conductor, will hardly entitle it to the name of an electric. CHAP. IV. _Of the electrical machine._ Having now explained the terms made use of in the study of electricity, and noted some of the phenomena of different electric substances, and the difference between electrics and conductors; we shall proceed to describe the _electrical machine_ made use of for shewing experiments, and for exhibiting other electric phenomena to the best advantage. The principal parts of the machine are, _the electric_, _the rubber_, the _moving engine_, and the _prime conductor_. We shall take notice of each of these parts separately and then describe the whole machine together.