An elementary book on electricity and magnetism and their applications . her with the reasonsfor many other highly important laws, the explanations ofwhich are now among the profound secrets of nature. The following table gives a list of materials placed approxi-mately in the order of their conducting powers: 1. Metals. 6. Pure water. 12. Shellac. 2. Charcoal, coke, and 7. Various oils. 13. Vulcanite. graphite. 8. Dry wood. 14. Paraffin. 3. Acids. 9. Silk. 15. Porcelain. 4. Salt solutions. 10. India rubber. 16. Glass. 5. Plants and animals. 11. 17. Dry air. 32 ELECTRICITY AND MAGNETISM
An elementary book on electricity and magnetism and their applications . her with the reasonsfor many other highly important laws, the explanations ofwhich are now among the profound secrets of nature. The following table gives a list of materials placed approxi-mately in the order of their conducting powers: 1. Metals. 6. Pure water. 12. Shellac. 2. Charcoal, coke, and 7. Various oils. 13. Vulcanite. graphite. 8. Dry wood. 14. Paraffin. 3. Acids. 9. Silk. 15. Porcelain. 4. Salt solutions. 10. India rubber. 16. Glass. 5. Plants and animals. 11. 17. Dry air. 32 ELECTRICITY AND MAGNETISM We ordinarily restrict the term conductor to the metalsand to carbon in the forms of charcoal, coke, and materials in the table numbered from 3 to 6 may becalled partial conductors/ and the last eleven materials maybe called insulators. Of all the materials named, dry airmay be said to be the only one which has absolutely no conduct-ing power under ordinary conditions, although that of glass,porcelain, etc., is exceedingly small at ordinary Fig. 17. — A bell circuit in a house. But even dry air, when under the stress of very high voltages,becomes a partial conductor. Chemically pure water and ice are practically presence of a very slight percentage of impurities, however,renders water a partial conductor. Since water found in natureis never absolutely free from impurities, all natural water isa partial conductor. For this reason a film of moisture uponan insulator greatly reduces its insulating quality. By means of the conducting property, or conductance, of metals,electric currents may be readily conducted from place to place. Forinstance, if a battery of several dry cells is located in the cellar of ahouse, a push button is located at the front door, and an electric bellis located in the kitchen, a metal wire may be led from one terminalof the battery to the push button, another wire may be led from thepush button to the bell,
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmagnetism, bookyear19
