The hard rubber lid bears the words: "1 Ohm (ligal); Temperature 11º1; 1796-6; J. Carpentier Ingr. constrr-Paris".
Contained inside a brass cylinder (diameter 6.5 cm, height 9.6 cm), closed with an hard rubber lid, it is sealed with a lead seal bearing the initials of the builder. The lid has a small hole, with a cork gasket, for the insertion of a thermometer; two large cylindrical copper conductors, bent into a U and held parallel by a spacer composed of two isolating plates of hard rubber, allow external connections.