[Electric engineering.] . passing through them. Fig. 3 shows a pin for thiskind designed by F. Locke, with a heavy insulator forcarrying a cable in the groove a. INSULATORS. 8. Insulators in this country are usually made of glass,while in Europe porcelain is more commonly used. Porcelain, when new, is a better insulatorthan glass; but it is more costly,and under the action of cold theglazed surface becomes this happens, the moisturesoaks into the interior structure,did its insulating quality isgreatly impaired. Tests re-cently made have shown thatwhen newly put up, the insula-tion
[Electric engineering.] . passing through them. Fig. 3 shows a pin for thiskind designed by F. Locke, with a heavy insulator forcarrying a cable in the groove a. INSULATORS. 8. Insulators in this country are usually made of glass,while in Europe porcelain is more commonly used. Porcelain, when new, is a better insulatorthan glass; but it is more costly,and under the action of cold theglazed surface becomes this happens, the moisturesoaks into the interior structure,did its insulating quality isgreatly impaired. Tests re-cently made have shown thatwhen newly put up, the insula-tion resistance of porcelain insu-lators io from 4 to 8 times betterthan glass, but that along rail-roads and in cities smoke forms athin film upon each material, sothat at the end of a few monthstheir insulating properties are nearly alike. On countryroads, away from railroad tracks, the porcelain insulatorsmaintain a higher insulation than the glass during rainstorms, but in fine weather it is not so high. Porcelain has an. Flu. 3. 15 ELECTRIC TRANSMISSION. advantage over glass in that it is not so brittle, and, there-fore, less likely to break when subjected to mechanicalshocks. Porcelain does not condense and retain on its sur-face a thin film of moisture so readily as glass, i. e., it isless hygroscopic. On the other hand, however, glass insu-lators are not subject to such an extent as porcelain to theformation of cocoons and cobwebs under them, the transpar-ency of the glass serving to allow sufficient light to passthrough the insulator to render it an undesirable abode forspiders and worms. As cocoons, cobwebs, etc. serve tolower the insulation of the line to a great extent, this is anadvantage that, in this country, it is not well to overlook. 9. Types of Insulators. — For ordinary work withmoderate pressures, glass insulators are used. The style ofinsulator will depend to some extent on the size of wireto be supported. Most power-transmission lines are ofweather-proof wi
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