104 Mr. Michael Faraday on some 



ference. With the exception of the above sentence I have 

 found no anticipation of my results, and as far as my own 

 knowledge and inquiries extend, am justified in giving them 

 as new. 



XIX. On some supposed forms of Lightning. By Michael 

 Faraday, D.C.L., F.K.S. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



THE magnificent display of lightning which we had on the 

 evening of the 27th of last month, and its peculiar ap- 

 pearance to crowds of observers at London, with the conse- 

 quent impressions on their minds, induces me to trouble you 

 with a brief letter on certain supposed appearances and forms 

 of lightning, respecting which the judgment of even good ob- 

 servers is often in error. 



When, after a serene sky, or one that is not overcast, thun«- 

 der-clouds form in the distance, the observer sees the clouds 

 and the illumination of the lightning displayed before him as 

 a magnificent picture; and what he often takes to be forked 

 lightning (i. e. the actual flash, and not a reflexion of it), ap- 

 pears to run through the clouds in the most beautiful manner. 

 This was the case on that evening to those who, being in Lon- 

 don, observed the storm in the west, about nine o'clock, when 

 the clouds were at a distance of twenty miles or more; and I 

 have very frequently observed the same effect from our south- 

 ern coasts over the sea. In many of these cases, that which is 

 thought to be the electric discharge is only the illuminated 

 edge of a cloud, beyond and behind which the real discharge 

 occurs. It is in its nature like the bright enlightened edge 

 which a dark well-defined cloud often presents when between 

 the sun and the observer; and even the moon also frequently 

 produces similar appearances. In the case of its production 

 by lightning and distant clouds, the line is so bright by com- 

 parison with the previous state of the clouds and sky, so sud- 

 den and brief in its existence, so perfectly defined, and of such 

 a form, as to lead every one at the first moment to think it is 

 the lightning itself which appears. 



But the forms which this line assumes, being dependent on 

 the forms of the clouds, vary much, and have led to many 

 mistakes about the shape of the lightning flash. Often, when 

 the lightning is supposed to be seen darting from one cloud 

 to another, it is only this illuminated edge which the observer 

 sees. On other occasions, when he was sure he saw it ascend, 



