Leyden jar
A Leyden jar (or Leiden jar, or archaically, Kleistian jar) is an electrical component that stores a high-voltage electric charge (from an external source) between electrical conductors on the inside and outside of a glass jar. It typically consists of a glass jar with metal foil cemented to the inside and the outside surfaces, and a metal terminal projecting vertically through the jar lid to make contact with the inner foil. It was the original form of the capacitor[1] (also called a condenser).[2]
Its invention was a discovery made independently by German cleric Ewald Georg von Kleist on 11 October 1745 and by Dutch scientist Pieter van Musschenbroek of Leiden (Leyden), Netherlands in 1745–1746.[3]
The Leyden jar was used to conduct many early experiments in electricity, and its discovery was of fundamental importance in the study of electrostatics. It was the first means of accumulating and preserving electric charge in large quantities that could be discharged at the experimenter's will, thus overcoming a significant limit to early research into electrical conduction.[4] Leyden jars are still used in education to demonstrate the principles of electrostatics.
Previous work[edit]
The Ancient Greeks already knew that pieces of amber could attract lightweight particles after being rubbed. The amber becomes electrified by the triboelectric effect, mechanical separation of charge in a dielectric material. The Greek word for amber is ἤλεκτρον ("ēlektron") and is the origin of the word "electricity".[5] Thales of Miletus, a pre-Socratic philosopher is thought to have accidentally commented on the phenomenon of electrostatic charging, due to his belief that even lifeless things have a soul in them, hence the popular analogy of the spark.[6]
Around 1650, Otto von Guericke built a crude electrostatic generator: a sulphur ball that rotated on a shaft. When Guericke held his hand against the ball and turned the shaft quickly, a static electric charge built up. This experiment inspired the development of several forms of "friction machines", which greatly helped in the study of electricity.
Georg Matthias Bose (22 September 1710 – 17 September 1761) was a famous electrical experimenter in the early days of the development of electrostatics. He is credited with being the first to develop a way of temporarily storing static charges by using an insulated conductor (called a prime conductor). His demonstrations and experiments raised the interests of the German scientific community and the public in the development of electrical research.
Further developments[edit]
Within months after Musschenbroek's report about how to reliably create a Leyden jar, other electrical researchers were making and experimenting with their own Leyden jars.[19] One of his expressed original interests was to see if the total possible charge could be increased.[20]
Johann Heinrich Winckler, whose first experience with a single Leyden jar was reported in a letter to the Royal Society on 29 May 1746, had connected three Leyden jars together in a kind of electrostatic battery on 28 July 1746.[21] In 1746, Abbé Nollet performed two experiments for the edification of King Louis XV of France, in the first of which he discharged a Leyden jar through 180 royal guardsmen, and in the second through a larger number of Carthusian monks; all of whom sprang into the air more or less simultaneously. The opinions of neither the king nor the experimental subjects have been recorded.[22]
Daniel Gralath reported in 1747 that in 1746 he had conducted experiments with connecting two or three jars, probably in series.[21]
In 1746–1748, Benjamin Franklin experimented with charging Leyden jars in series,[23] and developed a system involving 11 panes of glass with thin lead plates glued on each side, and then connected together. He used the term "electrical battery" to describe his electrostatic battery in a 1749 letter about his electrical research in 1748.[24][25] It is possible that Franklin's choice of the word battery was inspired by the humorous wordplay at the conclusion of his letter, where he wrote, among other things, about a salute to electrical researchers from a battery of guns.[26] This is the first recorded use of the term electrical battery.[21] The multiple and rapid developments for connecting Leyden jars during the period 1746–1748 resulted in a variety of divergent accounts in secondary literature about who made the first "battery" by connecting Leyden jars, whether they were in series or parallel, and who first used the term "battery".[21] The term was later used for combinations of multiple electrochemical cells, the modern meaning of the term "battery".
The Swedish physicist, chemist, and meteorologist Torbern Bergman translated much of Benjamin Franklin's writings on electricity into German and continued to study electrostatic properties.[27]
Starting in late 1756, Franz Aepinus, in a complicated combination of independent work and collaboration with Johan Wilcke,[28] developed an "air condenser", a variation on the Leyden jar, by using air rather than glass as the dielectric. This functioning apparatus, without glass, created a problem for Benjamin Franklin's explanation of the Leyden jar, which maintained that the charge was located in the glass.[29]
Capacity[edit]
The Leyden jar is a high-voltage device; it is estimated that at a maximum the early Leyden jars could be charged to 20,000 to 60,000 volts.[40] The center rod electrode has a metal ball on the end to prevent leakage of the charge into the air by corona discharge. It was first used in electrostatics experiments, and later in high-voltage equipment such as spark-gap radio transmitters and electrotherapy machines.
Originally, the amount of capacitance was measured in number of 'jars' of a given size, or through the total coated area, assuming reasonably standard thickness and composition of the glass. A typical Leyden jar of one pint size has a capacitance of about 1 nF.
Uses[edit]
Beginning in the late 18th century it was used in the Victorian medical field of electrotherapy to treat a variety of diseases by electric shock. By the middle of the 19th century, the Leyden jar had become common enough for writers to assume their readers knew of and understood its basic operation. Around the turn of the century it began to be widely used in spark-gap transmitters and medical electrotherapy equipment.
The development of the new technology of radio in the early 20th century encouraged the reduction in the size of Leyden jars as well as the reduction of undesired inductance and resistance. These improvements along with improved dielectrics caused the Leyden jar to evolve into the modern compact form of capacitor.