PROFESSOR LOVERING'S ADDRESS. 203 



mechanics for describing and explaining these strange and nameless 

 curves ; and, in acoustics, the ear has been dispossessed by the eye of 

 what would seem to be its own by right divine, and it is no longer the 

 best scientific judge of sounds. By new devices Koenig has trans- 

 lated time into space, and made visible the individual vibrations of 

 the invisible air; and, in numerous ways, the mechanism of sound is 

 as real to the eye as the sensation is to the ear. 



With a bare allusion to the fact that every message which passes 

 over the cable-telegraph is a tribute of indebtedness to the simple but 

 comprehensive method of Poggendorff, I pass to two other cases of 

 great difficulty and wide significance in which the same method has 

 triumphed. I refer to the determination of the velocity of electricity 

 and the velocity of light. 



When Wheatstone devised and executed the ingenious experiment 

 of producing three electrical sparks, not strictly at the same instant, 

 but after the brief interval required by electricity to travel over one- 

 quarter of a mile of copper wire, and then observing, not the sparks 

 themselves, but their images, as seen in a mirror revolving with the 

 prodigious volocity of 800 turns in a single second, and from the pro- 

 longation and relative displacement of these images deducing the ve- 

 locity of electricity, the duration of the electrical light, and the duality 

 in the direction of the transmitted disturbance, he delio-hted the 

 brotherhood of science by the skill and boldness of his attempt, and 

 astonished it by the extravagance of his results. For twenty years no 

 one ventured to repeat the difficult experiment. When it was finally 

 tried by Feddersen, and more recently by our own associate, Rood, 

 the values which they assigned to the duration of the electrical light, 

 and which could not be challenged, made still the wonder grow. So 

 far as this mode of experimenting concerns the velocity of electricity, 

 Wheatstone stands alone, and his estimate of this velocity (the largest 

 known velocity in the universe unless we count in the velocity of 

 gravitation) has never been brought to a second trial. Indirectly, it 

 has been tested by some of the operations conducted upon land and 

 ocean lines of telegraph. When the local times of two places are com- 

 pared by means of electro-magnetic signals, sent alternately in opposite 

 directions, the difference of longitude and the transmission-time of 

 electricity can be disentangled from one another, by the strategy of 

 mathematics, and the most probable value computed for each. The 

 velocity which has been calculated from these longitude-campaigns 

 falls far below that credited to Wheatstone. The apparent discrepancy 

 is explained by a misinterpretation of Wheatstone's experiment. An 

 experiment which proves that electricity runs through one-quarter of a 

 mile of wire at the rate of 288,000 miles a second, does not justify the 

 inference that it would move over 288,000 miles in one second. Anom- 

 alous as the case may be, electricity has no velocity in the ordinary 

 sense. The transmission-time of the electrical disturbance is propor- 



