A mahogany frame with a millimeter scale on the upper cross-piece carries four brass electrodes with rackwork and ending in pinchers. The two internal electrodes can also be adjusted sideways using the scale. With this apparatus for producing metalochromes, the physicist Leopoldo Nobili could compare the electrochemical deposition produced by two currents of the same or unequal strengths by having two pairs of electrodes in a common bath. Provenance: Lorraine collections.