322 Professor Oliver Lodge [June 1, 



immensely greater in every way than that of several who have made 

 more noise. 



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 demon- 

 strate 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,* 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. 



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, though time at present is very far from 

 being " infinitely long." 



The simplest way will be for me hastily to summarise our know- 

 ledge of the subject before the era of Hertz. 



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. 



If, on the other hand, the receiving body has a persistent period 

 of vibration, continuing in motion long after it is left to itself, Fig. 2, 

 like another tuning fork or bell, for instance, then far more facility of 

 response exists, but great accuracy of tuning is necessary if it is to be 

 fully called out ; for if the receiver is not thus accurately syntonised 

 with the source, it fails more or less completely to resound. 



* Phil. Mag., xxvi. pp. 229, 230, August 1888 ; or " Lightning Conductors 

 and Lightning Guards" (Whittaker), pp. 104, 105; also Proc. Rov. Soc, vol. 50, 

 p. 27. 



