The hot junction is allowed to attain these temperatures successively, and the corresponding deflection in each case is noted. It is then possible to divide up the whole of the scale to read temperatures directly. The first reading is taken by placing the junction in a vessel of boiling water, and for a locality near sea level it is not necessary in ordinary work to take account of fluctuations in the boiling point due to alterations of atmospheric pressure. To ensure that the other readings are taken when the substances are exactly at the melting point, the procedure is as follows: about 2-3 lb. of the substance are melted in a salamander crucible, and a small fireclay tube, closed at one end, is inserted in the molten mass. The hot junction is placed in the fireclay tube, and the intervening space filled with asbestos fibre. Great care must be taken not to let the junction touch the fused substance. The crucible is now allowed to cool, and a reading of the deflection taken every half-minute. When the substance is exactly at its solidifying point—identical in general with the melting point—the deflection remains stationary for several consecutive readings, owing to the liberation of latent heat of fusion in sufficient quantity to balance the loss by radiation. This stationary reading is noted for each substance, and represents the deflection given when the hot junction is at the temperature corresponding to the melting point, and the cold junction or junctions at the temperature existing when the observation is made. For melting the materials, a Davies furnace with a large Teclu or Meker burner is convenient up to 850° C.; but to melt the copper a blast lamp is requisite. The molten mass may be allowed to cool in the furnace. From these observations a calibration curve may be drawn either for differences between hot and cold junctions, or for a steady temperature of the cold junctions. Two sets of data are appended to illustrate the procedure.