joule of Manchester was the first to verify Mayer's law quantitatively.
"The Mechanism of Life"
Stéphane Leduc
If this condenser is charged to 20,000 volts, we have stored up in it half a joule of electric energy, and the volume of the dielectric is 270 cubic centimetres.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming
Hence, to store up in a glass condenser electric energy represented by one joule at a pressure of 20,000 volts, we require 500 cubic centimetres of glass, and it will be found that if we double the pressure and double the thickness of the glass, we still require the same volume.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming