The present Paper forms a continuation of one presented to the Association a short time ago. The subject was first put prominently before the Association in Mr. Spottiswoode's Paper “On Beats and Combination Tones.” I subsequently showed some of the elementary experimental methods by means of which I attempted to deal with the questions raised. Since that time I have been placed in possession of much larger means for dealing with these questions. I propose to give to-day some account of the experiments and results I have since arrived at. The apparatus does not differ in principle from that formerly exhibited to you; and as the improvement in its efficiency is principally due to the introduction of a large bellows driven by a steam-engine, and the experiments themselves are not suitable for verification by an audience, I have not attempted to bring any of the apparatus here.