History of electrochemistry
In 1789, Franz Aepinus developed a device with the properties of a "condenser" (now known as a capacitor.) The Aepinus condenser was the first capacitor developed after the Leyden jar, and was used to demonstrate conduction and induction. The device was constructed so that the space between two plates could be adjusted, and the glass dielectric separating the two plates could be removed or replaced with other materials.
Two capacitor paradox
The two capacitor paradox or capacitor paradox is a paradox, or counterintuitive thought experiment, in electric circuit theory. The thought experiment is usually described as follows: 
Two identical capacitors are connected in parallel with an open switch between them. One of the capacitors is charged with a voltage of formula_1, the other is uncharged. When the switch is closed, some of the charge formula_2 on the first capacitor flows into the second, reducing the voltage on the first and increasing the voltage on the second. When a steady state is reached and the current goes to zero, the voltage on the two capacitors must be equal since they are connected together. Since they both have the same capacitance formula_3 the charge will be divided equally between the capacitors so each capacitor will have a charge of formula_4 and a voltage of formula_5. At the beginning of the experiment the total initial energy formula_6 in the circuit is the energy stored in the charged capacitor: 
At the end of the experiment the final energy formula_8 is equal to the sum of the energy in the two capacitors 
Thus the final energy formula_8 is equal to half of the initial energy formula_6. Where did the other half of the initial energy go?