300 Number of Electrostatic Units in the Electromagnetic Unit. 



analyzers, but with molecular solutions of the sulphates of 

 zinc and copper, showed that the intermedial space in the case 

 of the zinc sulphate was much the greater. Again, another 

 series with zinc sulphate showed that a zinc analyzer gave the 

 least intermedial space, iron greater, copper greater still, and 

 silver most of all. 



This method affords a simple means of demonstrating differ- 

 ences of chemical affinity ; but whether it is capable of giving 

 more than approximative measurements will require further 

 investigation to determine. In some cases secondary actions 

 are, of course, set up, so that the intermedial space would repro- 

 sent the initial electromotive force + or — any interfering 

 electromotive forces. 



Dulwich College, 

 August 1881. 



XXXVIII. On the Number of Electrostatic Units in the 

 Electromagnetic Unit. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



I BEG to ask you very respectfully to allow me to publish 

 a few lines regarding Dr. C. R. A. Wright's letter (the 

 August number of this Magazine) in connexion with my paper 

 (Phil. Mag. Dec. 1880). It is with the greatest regret that I 

 am again compelled to trouble you with the subject, simply 

 because of the mistakes (for which I feel extremely sorry) in 

 the simplest part of my paper, namely putting down the nume- 

 rical figures in the table (p. 434, Phil. Mag. Dec. 1880). It 

 should stand thus: — 



et. r. R. Rtana. 



44° 15 75 ohms 107*88 ohms 105-09 



42 45 80 „ 112-88 „ 104-34 



51 39 50 „ 82-88 „ 104-76 



.-. the mean value of R tan «= 104-73 x 10 9 (C.G.S.). 

 The truth was that I was trying the experiment first with 

 100 f ^ or T) ^ cnan g e d them to Ji I ohms to get more 



convenient deflections, and copied down wrong numbers from 

 my notebook. As the values of R tan a were several times 

 worked out and examined carefully before the paper was 

 written (a close agreement between themselves having been 

 observed), I was so certain of their accuracy that every time 

 I read the proof I passed over the table. As to the mistake 



