In a previous paper an account was given of a series of experiments demonstrating the thermal diffusion effect in mixtures of hydrogen and carbon- dioxide. The gas mixtures were passed through a separating device consisting of a glass tube down the middle of which ran a helix of platinum wire heated by a current. The gas was drawn off in two streams, one from near the hot helix, the other from the cooler outer parts of the tube. Analysis of the two gas streams by means of a differential katharometer showed that there was a tendency for the heavier carbon-dioxide molecules to move towards the cold side, and for the lighter hydrogen molecules to move towards the hot side, thus producing a difference in the distribution of the components of the mixture. Although the method was useful for showing the effect of varying the temperature or of altering the proportions of the two gases, it was not suitable for measuring the amount of separation produced with the hot and cold sides under definite temperature conditions. The extremes of temperature only were known, and not the actual temperatures of the hot and cold streams of gas.