Leiden Jar
   The Leiden jar is the earliest form of the condenser or capacitor. The jar allowed the electric fluid produced by an electrostatic machine to be accumulated and stored for future use. 

   The first jars were made independently in 1745 by Ewald Georg von Kleist in Germany and Pieter van Musschenbroek in Leiden, about 35 km southwest of Amsterdam . The woodcut shows van Musschenbroek's attempt to electrify water in a glass flask. The electric charge produced by the friction of the hands against the revolving glass sphere was picked off the surface of the glass by the hanging chain, and conveyed to the metal rod hanging in the water forming the inner conductor. Andreas Cuneus, a visitor to van Musschenbroek's laboratory is just about to touch the inner conductor with his his other hand, giving him a nasty shock. 
REF: Thomas B. Greenslade, Jr., "Nineteenth Century Textbook Illustrations LV, Discovery of the Leiden Jar", The Physics Teacher, 32, 536-537 (1994)
   The capacity of early Leiden jars was indicated by the liquid capacity of the jars on which the inner and outer coatings of tinfoil were glued. In this case, this Leiden jar that I photographed at the Royal Scottish Museum in Edinburgh in 1978 must have been a multiple-gallon model. Sonia Greenslade gives the scale of this jar.

 
   An alternate approach making very large capacity Leiden jars is to connect a number of capacitors in parallel. This makes the equivalent jar whose foil area is equal to the sum of the areas of the individual jars. Today we would say that the capacities of condensers connected in parallel are additive. 

   This fine example is at Yale University. The jars are probably of quart capacity, thus making a gallon jar.
   This set of nine jars connected in parallel is in the collection of Transylvania University in Lexington, Kentucky. 

   When a condenser this large is shorted, a loud sound is heard as the spark jumps through the air. The sound was said to resemble the discharge of a battery of guns. The name "battery" was thus attached to a collection of condensers, and then to a collection of electro-chemical cells. 
   This unmarked collection of four quart Leiden Jars is in the collection at Kenyon College in Ohio. The box holding them is lined with tinfoil, thus connecting the outer conductors together.

   I used a capacitance meter to measure C for one of these jars, and obtained a value of about 1200 pF. This agreed pretty well with a calculation of the equivalent flat-plate capacitor with a glass dielectric. When charged to 1000 V, this device will store about 0.06 J of energy.
   This set of Leiden jars is in the Garland Collection of Classical Physics Apparatus at Vanderbilt University.

   The jars are each about 24 cm in height, and are insulated from ground with glass rods. The binding posts on the bottom make it possible to connect the set either in series (to give a longer spark) and in parallel (to give a thicker spark).

   This is very likely a piece of French apparatus, as Chancellor Garland bought a good deal of French apparatus to outfit the new Vanderbilt University ca. 1875.
   This pair of unmarked Leiden jars are at Denison University in Granville, Ohio. They may have been made by students in the years 1890-1910 as part of their laboratory course. 

   The electrodes here are the interesting feature. Since one is pointed and one is spherical, I suspect that they might have been used in studies of  electrical discharges in the air. 

  This is Lane's Unit Jar and is in the apparatus collection of the University of Vermont. It is used to measure out equal quantities of electric fluid from an electrostatic machine to a large Leiden battery.

   The two electrodes are connected to the prime conductor of the electrostatic machine and the Leiden battery. When the charge on the unit jar builds up to a certain potential difference between the knobs of the spark gap, the spark jumps and the electricity is delivered to the battery. The total amount of charge delivered is thus measured by counting the sparks. The spark gap may be altered using the micrometer on the upper left-hand side. 

   The apparatus is unmarked, but it is almost identical with Lane's unit jar shown in the 1900 catalogue of Max Kohl of Chemnitz for 30 marks (about $7.00).
 







   This example of a Spotted or Diamond Jar is in the apparatus collection of Case Western Reserve University in Cleveland, Ohio. The outer coating is not quite continous, and as the jar is charged sparks can be seen jumping between the sharp tinfoil points. 

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