I owe to Mr Dewar's skill in manipulation the means of determining the line of sodium in the thermo-electric diagram. He constructed for me a long quill tube of German glass, with platinum wires inserted near the ends; exhausted it by means of a Sprengel pump, and drew in melted sodium from a bath of paraffin. Exact determinations will require considerable time, even with this excellent apparatus; but in the meantime I may state (as a first approximation) that the line of sodium is nearly parallel to that of palladium, and somewhat above it in the diagram.