Large wooden helical conductor covered with gold foil, on two glass pillars coated with red sealing-wax varnish. This type of varnish was much used with electrostatic apparatuses as it increased the electrical insulation of the glass, which, without the varnish, tended to attract more moisture. The instrument's inventor, Gaetano Cari, wrote a small book about his conductor (Nuovo Conduttore Spirale con la sua Teoria, Pistoia, 1783). He believed that his device could carry more charge than the conventional cylinder. In the engraving in his book, the helical conductor is suspended from the ceiling by silk cords. Provenance: Lorraine collections.