The central conductor is covered with several continuous coatings of guttapercha, the total weight of which varies between 70 and 650 lb to the mile.
In actual practice the receiving instrument is so sensitive that the difference of potential between the two coatings of the condenser C3 produced by the incoming signal is only a very small fraction of the potential of the battery B.
The famous cameo glass was formed by covering a mass of molten glass with one or more coatings of a differently coloured glass.
For if C l and C2 are the capacities and Q i and Q2 are the charges after contact, then Qi/CI and Q2/C2 are the potential differences of the coatings and must be equal.
If a charged condenser is suddenly discharged and then insulated, the reappearance of a potential difference between its coatings is analogous to the reappearance of a torque In the case of a glass fibre which has been twisted, released suddenly, and then gripped again at the ends.