The series of experiments here described had for their object the measurement of the variation in the Peltier effect due to change of temperature; they were made during the last six weeks. The arrangement which I used in these experiments was suggested by a form of apparatus used in Professor Tait's laboratory; the following is a description of it. A plate of sheet lead (say) is bent into the shape of an arch (∩-shaped), and to its lower edges are soldered two plates of sheet-iron, to the opposite edges of which are soldered three or four copper wires proceeding to mercury-pools, which can be put into connection with a battery.