Definition
An early form of capacitor consisting of a glass jar coated on the inside and outside with metal foil, separated by the glass dielectric. It stores an electrical charge between the two foil layers and can release that charge when the layers are connected through an external circuit.
Plain English
A glass jar with metal foil on the inside and outside that holds an electrical charge. It was the first device ever built that could store electricity for later use.
Context Anchor
Seen in basic aircraft electricity discussions when explaining stored electrical charge, capacitance, and older ignition or radio theory.
Derivation
Named after Leyden (now Leiden), the city in the Netherlands where it was invented in the 1740s at the University of Leyden. Knowing the name is just a place reference helps the reader recognize that a Leyden jar isn't a special type of jar — it's simply where the device was first built.
Why Pilots Care
Pilots and technicians don't use Leyden jars themselves, but understanding the device makes the operation of modern capacitors in aircraft electrical and ignition systems easier to grasp — same principle, smaller package.
Grounding Statement
A Leyden jar stores electric charge by keeping opposite charges separated on two metal surfaces with glass between them.
Intuition Check
Do not picture a jar that stores fluid. A Leyden jar stores electric charge.
Example Sentence 1
The instructor used a Leyden jar demonstration to show how a capacitor stores and releases electrical energy.
Example Sentence 2
A student pilot reading about basic electricity principles may encounter a description of charge building up inside a Leyden jar.