ELECTRICAL WAVES. 513 



and, if now the Ruhmkorff be excited, a series of stationary elec- 

 trical waves will be formed in the wire. To detect these we em- 

 ploy the principle of resonance. A wire whose time of oscillation 

 has been determined and found to be nearly equal to that of the 

 primary conductor is bent into a circle, and the ends are brought 

 close together. This is then brought close to the long wire, and 

 held so that its plane embraces the latter. A fine display of sparks 

 will be seen to accompany the Ruhmkorff discharge. 



If this proof circuit be approached to the extreme end of the 

 long wire, no sparks will be seen. The wire has at its end, in fact, 

 a node the same as a stopped organ-pipe has. As the air in the 

 pipe is undisturbed, so the potential of the wire end is unchange- 

 able. As we recede from the end, the sparks grow longer, but 

 finally disappear again. Here is another node. We measure the 

 distance between the two and cut the wire so that its total length 

 shall be a multiple of this length, and then we proceed to find all 

 the nodes, and mark them by paper riders. If we measure each 

 of these distances and take the mean, or measure the whole length 

 of the wire and divide by the number of nodes, we have a value 

 for the wave-length of the conductor. In Hertz's experiment this 

 value was 2'8 metres. From this value, and the time of oscilla- 

 tion reckoned from the self-induction and capacity, he gets the 

 velocity of propagation of electrical disturbances as two hundred 

 thousand kilometres per second. This result Hertz prints in 

 bold-faced type, and puts it as a climax of all his work. This is 

 truly wonderful. If we consider that the calculated value of the 

 time of oscillation depends upon the assumption that the velocity 

 of electrical wave propagation is the same as that of light (three 

 hundred thousand kilometres per second), and this circuitous 

 calculation of the same thing gives two hundred thousand kilo- 

 metres per second, we can hardly give Hertz the credit of ex- 

 tremely accurate work. However, Hertz has made a great ad- 

 vance in physical science. Since Weber introduced the absolute 

 system of units, no great advance has been made. Physicists have 

 busied themselves in measuring the various constants, in refining 

 and perfecting the methods of measurement, or in applying prin- 

 ciples already known to technical and practical purposes. Hertz, 

 however, has opened a new and unexplored field, which must 

 eventually bring us into a closer acquaintance with the mysteries 

 which we are daily manipulating. 



This series of experiments has excited a great deal of attention 

 in English physical circles. Prof. Fitzgerald, of this department 

 of the British Association, laid great emphasis, at the last meet- 

 ing, on the advance which had been made. Oliver Heaviside has 

 justified his patronymic by publishing a complex mass of mathe- 

 matical formulae on the subject. He considers that the waves of 



vol. xxxv. — 33 



