products of his labor, but to use these in the presence of physicists and to show practically the value of the graphic method of studying harmonic motion which had grown almost to perfection in his hands. The mathematical analysis of wave-motion had been abundantly brought out in technical treatises. Dr. Thomas Young, in the beginning of the present century, had pointed out the method by which a tuning-fork might be made to trace a record of its own vibrations, and his hint was put into practice nearly half a century afterward by Wertheim and Duhamel. But Koenig was the first to apply this method systematically to the registration of not only simple vibrations but also compound harmonic motion; and a large variety of such phonograms executed with apparatus of his device, and accompanied with the tracings of the corresponding theoretical curves, attracted much attention at the exhibition. The method has since been adopted in a number of other fields, notably in physiology for the analysis of animal motion, and in general physics for the measurement of minute intervals of time.
At the same exhibition in 1862 Koenig exhibited a wholly new method of making the effects of sonorous vibration easily visible by utilizing the delicate sensitiveness of flame to variations of atmospheric pressure. Four years earlier some noteworthy experiments had been made in America by Le Conte on the effect of such vibrations upon naked gas-flames; but no development had thus far been evolved from them. Koenig devised the manometric capsule through the medium of which the pressure at the outflowing jet is modified at will by sound-waves conducted to an elastic membrane. The motion of this produces pulsations in the gaseous fuel, and their effect on the flame is observed by looking at its image reflected from a revolving mirror. This beautiful method has been applied by its originator with much success to the study of the interference of sound, and to the investigation of the quality of musical sounds. No two vowels can be sung in succession to the delicate flame without impressing on it their separate individuality; and the eye is thus permitted to compare differences which the ear may recognize but not analyze. To see one's own voice in a mirror, to watch the successive phases of melody and harmony, to see two sounds interfering and producing visible silence—these are some of the revelations of the manometric flame.
This remarkable exhibition of Koenig's originality brought him prominently into notice everywhere. A detailed description of his work was published soon afterward by Prof. Tisko in Vienna, and from that day to this he has had no rival in the field which he had made his own. In every university where acoustics is taught Koenig's apparatus is the standard. Honors also were