On Rapid Electrical Oscillations. 297 



is true or not, that the greater part of our paper is taken up 

 by a discussion as to the limits within which this proposition 

 is true, that our results (much more numerous than Mr. 

 Skinner's) are illustrated by two sheets of curves (plates xii. 

 & xiii.), and, finally, that a method of determining high 

 specific resistances based on this property of Clark cells has 

 been in use almost daily in our laboratory since the paper 

 was written in 1888, and was described by us (Phil. Mag. 

 1889, vol. xxviii. p. 470) — considering all this, I say that 

 Mr. Skinner's unconditioned statement of his conclusion 

 appears to me to be somewhat inadequate. 



There is yet another point. On page 273, and referring 

 to the measurement of the resistance of his cells, Mr. Skinner 

 says : — "However, following Mr. Fitzpatrick's method, tests 

 were specially made for polarization by varying the ratio of 

 the arms and by varying the speed of the commutator." So 

 far as varying the speed of the commutator goes, this method 

 was described to all intents and purposes by Kohlrausch in 

 Pogg. Ann., Jubelband, p. 290, in Wiedemann's Electricitdt, 

 vol. i. p. 476, and, I think, in Professor Chrystal's article in 

 the Encyclopaedia Britannica. It is therefore a mistake to 

 ascribe it to Mr. Fitzpatrick. 



R. Theelfall. 



Sydney, December 30, 1894. 



XXVIII. Value of the Magnetic Permeability for Rapid 

 Electrical Oscillations. 



To the Editors of the Philosopliical Magazine. 

 Gentlemen, 



THERE have been various estimations of the above quan- 

 tity, but the results resting upon experimental data are 

 few. A late paper by Ignaz Klemencic in \Vied. Ann. der 

 Physik und Chemie, JSTo. 12, 1894, contains the following 

 values of the permeability in case of oscillations of 1,000,000 

 per second: — 



Soft iron .... /z,= 118, 



Steel ..... ^=106 to 115. 



In a paper in the Philosophical Magazine for Xovember 

 1894, on " Wave-Lengths of Electricity on Iron Wires," I 



