It was my pleasant duty to deliver a discourse at the Royal Institution, on Friday week last, on the general subject of musical pitch, and its mode of determination. Our excellent Secretary, who was there, was kind enough to say that he thought a practical application of the scientific principles then laid down might be interesting to this Society, and I propose to do what the short period allowed for lectures at the Royal Institution did not allow me to do, namely, to carry one degree further into the artistic department the principles then enunciated. It is no use, as was remarked to me by more than one distinguished musician present, telling us all this, unless you can give some rules by which to prevent discords and discrepancies. Now I shall endeavour to take up the tail end of that lecture, and fasten on it a still longer tail of a practical character. I have put up, however, the large diagram which served as a resumé in my former lecture, showing the methods of determining musical pitch. For many centuries there was no definite pitch; then the pitch settled down, and for a considerable period remained—during the time of Beethoven and Mozart, and many of our great writers—tolerably steady. With the increase of the orchestra—with the multiplication of the means of producing sound—there came a very rapid rise in pitch, and this rise has been so rapid that since the time of Handel, as has been shown by Mr. Ellis in his learned and valuable papers, it has gone up at least a semitone; nor is there any finality observable in this matter; it might seem as if the pitch would go on rising with the same expeditiousness from causes which are still in operation and which caused the present rise. We cannot go into that part of the subject. We have at last determined a standard. Of the various methods on the diagram, some of the latter seem so satisfactory that we may say that we have a pitch. We have a standard just as the French have their mètre; as the second is the measure of time; as there are now standards of electric measurement; so I think at last in some of the instruments here named, Scheibler's tonometer, Appunn's reed tonmesser, and Koenig's tuning-fork clock, we may be said to have a unit of measure like the British yard or the mètre.