Lord Rayleigh on the Theory of Resonators, 419 



when the loss of charge is soon rendered visible on both sides ; 

 but as the lengths on A and B may be very unequal, the rush 



—EARTH 



of current alone will not enable us to say on which side the fault 

 may be; but by carefully watching the electrification for an 

 equal time on each side, no difficulty will be found in fixing 

 upon the drum containing the fault. 



Two or more faults existing together form no embarrassment 

 to the test. All to be done is, if the faults are of unequal mag- 

 nitude, to remove the more extensive first, or to keep one side 

 right by removing the faults as they are coiled over to it. In 

 any case the battery-power required will vary with the magni- 

 tude of the fault and the sensitiveness of the instrument. 



Tarn worth House, 

 Mitcham Common. 



LIII. A Contribution to the Theory of Resonators, 

 By Lord Rayleigh, M.A., F.R.S.* 



THE following paper is an extract from a work on Acoustics 

 on which I have been for some time engaged ; on this 

 account it is not quite self-contained, but will, I hope, be found 

 sufficiently intelligible. Most of the materials have already been 

 in my possession upwards of a year ; and the interest of the sub- 

 ject seemed to render further delay in publication unadvisable. 

 Unfortunately the rapid completion of my book has been much 

 interfered with by various causes of a private character. 



The operation of a resonator when under the influence of a 

 source of sound in tune with itself, has been the subject of much 

 misapprehension, from which even Helmholtz does not appear 

 to have been free. In a dictionary of science we read : — " The 

 loudness of the sound produced by a sounding body is augmented 

 by bringing the body into the neighbourhood of a column of air 

 which is capable of vibrating in unison with itself "f. Now this 

 statement, though true in certain cases, as, for example, when a 

 tuning-fork is held over a resonator, requires, to say the least, 

 serious limitation. The exceptions, if not more frequent, are, 



* Communicated by the Author. 

 f Dictionary of Science. Rodwell. Art. Resonance. 

 2E2 



