His best known discovery is by no means his only one, and no less than eighteen Papers were contributed to German periodicals by him, in addition to the papers incorporated in his now well-known book on electric waves. In closing these introductory and personal remarks, I should like to say that the enthusiastic admiration for Hertz’s spirit and character felt and expressed by students and workers who came into contact with him is not easily to be exaggerated. Never was a man more painfully anxious to avoid wounding the susceptibilities of others; and he was accustomed to deprecate the prominence given to him by speakers and writers in this country, lest it might seem to exalt him unduly above other and older workers among his own sensitive countrymen. Speaking of the other great workers in physics in Germany, it is not out of place to record the sorrow with which we have heard of the recent death of Dr. August Kundt, Professor in the University of Berlin, successor to Von Helmholtz in that capacity. When I consented to discourse on the work of Hertz, my intention was to repeat some of his actual experiments, and especially to demonstrate his less-known discoveries and observations. But the fascination exerted upon me by electric oscillation experiments, when I, too, was independently working at them in the spring of 1888,[1] resumed its hold, and my lecture will accordingly consist of experimental demonstrations of the outcome of Hertz’s work rather than any precise repetition of portions of that work itself. [1] _Phil. Mag._, XXVI., pp. 229, 230, August, 1888; or “Lightning Conductors and Lightning Guards,” pp. 104, 105; also _Proc. Roy. Soc._, Vol. 50, p. 27. In case a minority of my audience are in the predicament of not knowing anything about the subject, a five minutes’ explanatory prelude may be permitted; and the simplest way will be for me hastily to summarise our knowledge of the subject before the era of Hertz. [Illustration: FIG. 1.--Oscillations of Dumb-bell Hertz Vibrator (after Bjerknes).] Just as a pebble thrown into a pond excites surface ripples, which can heave up and down floating straws under which they pass, so a struck bell or tuning fork emits energy into the air in the form of what are called sound waves, and this radiant energy is able to set up vibrations in other suitable elastic bodies. If the body receiving them has its natural or free vibrations violently damped, so that when left to itself it speedily returns to rest (Fig. 1), then it can respond fully to notes of almost any pitch. This is the case with your ears and the tones of my voice. Tones must be exceedingly shrill before they cease to excite the ear at all.