When Mr. Spottiswoode asked me some time since to take his place in reading a paper before this Society, I called to mind some acoustical experiments I made last summer, with a view to making out how we detect so easily and generally the direction of a source of sound, and hoped to be able to complete the experiments to some extent, so that I might be able to present the matter in a little more complete form. Unfortunately, however, my health is not good enough to allow of my making acoustic experiments in the open air at this time of the year, and therefore I have but little to add to what I discovered last summer.