I come before you once more as the advocate of the Substantial Theory of Sound, and as a letter-in of light upon some of the fallacies and impossibilities of the time-honored mechanical theory, commonly called the Wave Theory of Sound. I come before you with most pleasant recollections of your courteous and patient hearing on the previous occasion, when I introduced the Substantial Theory to your notice for the first time. I took you somewhat by surprise on that occasion, for the subject was new to you; and few were prepared to question, at the moment, the bold statements I then made, to discuss the arguments I advanced, or to see the full force and teaching of the experiments I performed. Now, however, matters are different, for you have had full opportunity of reading and considering my first paper; and many of you have either heard or read my good friend Dr. Pearce's admirable lecture. Some present may have listened to my second lecture, delivered on November 8th, before the National Society of Professional Musicians; and now, with so much additional information and thought, it is probable you have come to some conclusion in your own minds. If, as musicians, you have been content to reflect on your daily experience in matters of sound, and have elected to use the reasoning powers and to exercise the common sense God has given you with an open and unprejudiced mind, I know very well, from my own experience, towards which theory you incline; but if, on the other hand, you have shut your ears to your daily experience, and have blindly pinned your faith to great names with their array of mathematical formulae, then I know how unsubstantial your theory is.