106 Mr. Martyn Roberts in reply to Prof. Poggendorff, 



which, when the lightning occurs amongst or beyond them, 

 present forms and lines before unperceived. 



The apparent duration, which I before spoke of, is merely 

 a case of very rapid recurrence, and may, by a careful ob- 

 server, be easily connected with that which I have now pro- 

 posed as the best test of the nature of the phenomenon. 



There are some other circumstances which will help to di- 

 stinguish the effect I have thus endeavoured to describe from 

 the true appearance of the lightning flash, as the apparent 

 thickness, sometimes, of the supposed flash, and its degree of 

 illumination; but I have, I think, said enough to call atten- 

 tion to the point; and, considering how often the philosopher 

 is, in respect to the character of these appearances, obliged to 

 depend upon the report of casual observers, the tendency of 

 whose minds is generally rather to give way to their surprise 

 than to simplify what may seem remarkable, I hope I have 

 not said too much. 



I am, Gentlemen, your obedient servant, 



June 22, 1841. M. Faraday. 



XX. Remarks on Professor Poggendorff's Paper on the In- 

 tensity of Current of the Zinc-iron Circuit. By Martyn 

 J. Roberts, Esq., F.K.S. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



CIRCUMSTANCES preventing my having access to your 

 Magazine, it was long after the publication of your 114th 

 Number that my attention was called to it as containing a 

 translation of Prof. Poggendorff's Memoir, read before the 

 Berlin Academy, upon the discovery made by me of an ano- 

 malous condition of iron in the galvanic circuit*. 



In this memoir the learned Professor states that I have 

 offered no opinion in explanation of the phenomenon, and that 

 indeed a satisfactory one could hardly be given with the pre- 

 sent views of electrical science in England. I must confess 

 myself to blame in not having given the experiments in greater 

 detail, as it might have prevented the mistake the learned 

 Professor has evidently fallen into as to the cause of the phe- 

 nomenon, and I trust the condition of electrical science in 

 England is not so low as to prevent our giving an explanation 

 of so simple a matter; indeed 1 am surprised that in repeating 

 my experiments the learned Professor did not at once per- 

 ceive the true solution of the apparent anomaly. 



In his memoir he appears to attribute the superiority of 

 the iron-zinc over the copper-zinc galvanic pair to some in- 



* Phil. Mag. Third Series, vol. xviii. p. 42. 



