﻿334 Intelligence and Miscellaneous Articles. 



The University of Melbourne. 

 25th October, 1911. 



To the Editors of the Philosophical Magazine. 



Gentlemen - , — 

 Tx the Proceedings of the Physical Society, vol. xxiii. part 5, 

 "which has just come to hand, I find that on June 9th, 1911, 

 Professor S. P. Thompson read a paper to the Physical Society 

 entitled " A New Method of Approximate Harmonic Analysis by 

 selected Ordinates." 



In the Philosophical Magazine for November 1903, I published 

 a " Preliminary Account of a Wave Tracer and Analyser" which 

 I had designed, and which carried out on actual live waves of 

 e.m.f. current, or magnetic flux, the process now brought forward 

 by Professor Thompson. In my paper the theory of this method 

 of Harmonic Analysis was given as bearing on the operation of 

 the Wave Tracer and Analyser, and it was shown that the method 

 was applicable to any periodic curve. 



Attention was also drawn to the fact that the method was 

 analogous to that of Wedmore, whose work Professor Thompson 

 does not seem to be acquainted with, but who was the first, so 

 far as I am aware, to apply to Harmonic Analysis the simple 

 method of adding and subtracting selected ordinates. 



When using the Wave Tracer and Analyser for magnetic 

 research, I found that it was quicker and more accurate to obtain 

 by its means the complete wave only, by observing a selected 

 number (usually 15) of its equi-spaced ordinates, and afterwards 

 to apply the method of analysis under discussion to these ordi- 

 nates. Having found the process very satisfactory, I thought 

 the kuowledge of it would be useful to others, and on December 8th 

 190J: I read a paper at the Royal Society of Victoria on "An 

 Expeditious Method of Harmonic Analysis," in which both the 

 theory and my practice of the method was fully explained. 

 This paper was afterwards printed in the Philosophical Magazine 

 for January 1906. 



Professor Thompson has certainly modified the practical 

 application of the method by an elegant device, i. e. of determining 

 two ordinates. in quadrature for each harmonic, thus obtaining 

 their amplitudes and phases by a method different from mine, 

 but in this no new principle is involved. 



Though I dislike raising questions of priority, I feel that the 

 title of Professor Thompson's paper is so misleading as to render 

 this letter necessary, for his method is not new but involves, at 

 most, an improvement on an old established method. 



Tours faithfully, 



Thomas E. Lyle. 



