This arrangement is called a voltaic pile (after its inventor, Volta), and the difference of potential produced is proportionate to the number of pairs of disks.
A difference of potential between two points connected will cause current to flow till the potentials of both points are the same.
ELECTRIC RESISTANCE.
Resistance is offered by all substances to the electric current, and varies with the nature of the substance.
Most metals are good conductors; wood and stone offer considerable resistance, and silk, glass and ebonite are practical non-conductors; but remember if a non-conductor is wet or even damp it becomes a good conductor, moisture or water being a first-class conductor. On the other hand, conductivity is diminished by an increase of temperature—otherwise dryness. The following table will give a good idea of the conductivity of metals:
| That of silver being | 100 |
| That of copper is | 97 |
| That of gold is | 74 |
| That of platinum is | 17 |
| That of iron is | 16 |
| That of lead is | 8 |
| That of German silver is | 7.5 |
| That of mercury is | 1.6 |
Therefore, generally, good conductors are all the metals, carbon, water, aqueous solutions, moist bodies besides wood, cotton, hemp, etc. Good insulators or non-conductors are paraffine, solid or liquid, turpentine, silk, sealing wax, india rubber, dry glass or porcelain. The best electrical conductors are the best thermal conductors, and a “red hot” temperature converts insulators into fairly good conductors.
ELECTRICAL MEASURES.
Electricity being invisible and imponderable (i. e., not having sensible weight, such as light, heat or electricity), it is impossible to apply ordinary standards of measure. Electricians have devised special units of measure of two kinds, called absolute units and practical units, the ratio between the two being always some power of 10.
It has been decided in these measurements, length, mass and time shall be expressed respectively in centimeters, grams and seconds—called C. G. S., or centimeter gram-second method.