344 Prof. A. Schuster on the 



result. Here it is assumed that the action of the oscillator 

 and of the wire singly are equivalent to the two together. 

 To examine this minimum more closely readings were taken 

 at intervals of one centimetre. There is no doubt of its 

 existence ; it is about 10 cms. from the end for the smaller 

 oscillators and slightly farther for the larger ones. I find it 

 difficult to give the significance of this. 



Other minima were found, but they were not so well 

 defined. They are, no doubt, due to natural oscillations of 

 the wire, but they are hard to identify. 



For the wires 300 and 400 cms. long the chief minima are 

 at the middle points. 



The question of the dependence of the positions of the 

 minima on the detector is interesting and important ; and 

 that there is no such connexion was shown in the following- 

 way. A second helix, similar to that of the detector, was 

 soldered to the free wire running up beside the one bearing 

 the wing, thus practically doubling the capacity and in- 

 ductance ; but there was no displacement of the minima. 

 The period of the detector must be many times that of the 

 oscillators. 



In the near future I hope to apply the magnetic detector 

 to the exploration of much longer wires, in which case the 

 phenomenon of standing waves should be more distinctly 

 shown. 



University of Toronto. 



XXXII. On the Spectrum of an Irregular Disturbance. 

 By Arthur Schuster. F.R.S* 



IX the February number of the Philosophical Magazine 

 Lord Rayleigh quotes under the above title the following 

 remark, which 1 made in a paper on the " Periodogram of 

 Magnetic Declination as obtained from the Records of the 

 Greenwich Observatory during the years 1871-1895 :" 



" Absolute irregularity would show itself by an energy- 

 curve which is independent of the wave-length, i. e., a straight 

 line when the energy and wave-length or period are taken as 

 rectangular coordinates, while the perfect regularity of homo- 

 geneous vibrations would show itself as a discontinuity in the 

 energy- curve." 



Discussing the same problem, Lord Rayleigh arrives at 

 the different conclusion that the energy of an arbitrary dis- 

 turbance is proportional to dk or k 2 dl-, according as the 

 * Communicated by the Author. 



