Electricity for public schools and colleges . til the restoringcouple, due to the twisting of the two paraUel silk fibres, is suffi-ciently great to give equilibrium. If the potential V of the needlebe known, and if the constants of the instrument be known, then the diflerence of potential(Vj — v.,) can be calculated fromthe observed deflexion. In the next figure we have asketch of the Elliott-pattern quad-rant electrometer ; a comparativelysimple form of instrument. Oneof the quadrants is represented asremoved, so that the needle may beseen. This needle is maintained ata high potential in som
Electricity for public schools and colleges . til the restoringcouple, due to the twisting of the two paraUel silk fibres, is suffi-ciently great to give equilibrium. If the potential V of the needlebe known, and if the constants of the instrument be known, then the diflerence of potential(Vj — v.,) can be calculated fromthe observed deflexion. In the next figure we have asketch of the Elliott-pattern quad-rant electrometer ; a comparativelysimple form of instrument. Oneof the quadrants is represented asremoved, so that the needle may beseen. This needle is maintained ata high potential in somewhat thefollowing manner. From it therehangs a platinum wire, dipping intoa glass vessel that contains strongsulphuric acid. Outside this vesselis a coating of tin-foil, so that it isin fact a Leyden jar. Its capacitybeing very great as compared with the capacity of an isolatedbody, it serves to maintain the potential of the needle approxi-mately constant for a considerable time. From the needle rises a light stem, bearing a small Fig. CH. X. ELECTROSTATIC POTENTIAL 157 The usual lamp and scale arrangement gives us, in the reflectedspot of light, a very sensitive means of noticing and measuring thedeflexions of the needle. Complete form of the quadrant electrometer.—In the completeform of Sir W. Thomsons quadrant electrometer there are manydetails of construction that we shall not discuss here. But wemust mention two of the most important of these. (i.) T/iegauge.—Connected with the inside of the Leyden jar(and so with the needle) is an attraded-disc electrometer. If theweights or spring be so arranged that the \i2\x {see § 32) is in theproper line of sight when the jar, needie, and disc/therewith con-nected, are at some fixed potential V, then any alteration in thispotential will be at once detected by the movement of the is one detail. (ii.) The replenisher.—The other detail is a replenisher (seeChapter VII. § 5), in which one armature is to eart
Size: 1266px × 1974px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpubl, booksubjectelectricity
