No offer of friendship was ever more welcome to me, and there never was a friendship of which I was more proud. Before many days had passed, the natives of Norfolk, from the illustrious Eldridge family, the angels of the town, down to the most humble day-laborer, felt the same toward me as old Nettleton did; that is, I always thought so, and I have never had any reason to think otherwise. No resolution moved by me at the annual town meetings ever failed to pass, but I always moved slowly, and not until I was quite sure that the motion was in the right direction. I would sooner have risked losing the good opinion of the trustees of Columbia University than that of the good people of Norfolk, my American Idvor. During my summer vacations in Norfolk, I have always felt just as much at home, and as happy and contented, as I did in my native Idvor when, during my student days in Europe, I spent my summer vacations there. Whenever I returned to my laboratory from my summer vacation in the bracing atmosphere of Norfolk, I have always felt that no problem there could resist the force of my stored-up nervous energy. That feeling early encouraged me in the belief that I had completely recovered from the breakdown of the spring of 1896, and this belief gave wings to every new effort. When the news of the discovery of the Roentgen rays reached me in December of 1895, I was busy with the research of a problem which I had taken up in 1894, while making a foot tour in Switzerland. This is the problem which I took up again after the recovery from the breakdown of 1896. I must confess here that I never returned to X-ray research, because for a long time after my illness even the sight of an X-ray tube made me almost hysterical. During the first half of the summer of 1894, Mrs. Pupin and I were staying at a little hotel on Lake Wannensee in Switzerland; I was preparing my lectures on the mathematical theory of sound. Lord Rayleigh’s treatise called my attention to the classical problem which ten years before I first saw in La Grange’s famous treatise. I had bought it second-hand in Paris, and had studied it in my mother’s garden at Idvor. The problem was a hypothetical one relating to an imaginary and not to a real physical case. It may be stated as follows: