This ingenious instrument was invented by James Sixe of Colchester and appears to have been manufactureed exclusively - and briefly - by Negretti and Zambra. It works through the expansion and contraction of the alcohol in the central bulb, alternately raising the indexes in the neighbouring sections of tube. These should be set at the top of the mercury using a magnet, and the instrument must be kept vertical to prevent mixture of the two liquids within. Negretti and Zambra claim it as the only thermometer applicable for determining the temperature of the sea at depths.