506 On the Persistent Appearance of the Lightning Flash. 



same throughout, and not to have varied from its original 

 strength. A similar experiment made with a solution of sul- 

 phuroi;s acid in water, gave results which showed that it remained 

 quite homogeneous. 



LXVI. On the Persistent Appearance of the Lightning Flash. 



Saturday, June 20th, 1857. 



THE thunder-storm which passed over London last night, 

 gave me an opportunity of repeating an observation on 

 lightning which I had before made on four or five occasions. As 

 the cause of the effect observed is, as far as I am concerned, only 

 guessed at, I publish this notice that it may attract attention so 

 that the effect may be verified ; and if verified, perhaps find an 

 exact explanation. Between 12 and 1 o'clock the storm was 

 over London. Much of the lightning was within the clouds. 

 At one moment the part of the heavens at which I was looking, 

 directly above me, displayed the lightning flash in irregular lines: 

 these formed in one part a large >- stretching across a space 60° 

 or more in extent ; beside which there were other lines of light- 

 ning not connected with this, but occurring at the same instant. 

 These lines did not disappear instantaneously, but faded away, 

 occupying, I think, a second or more before their extinction. 

 As they faded, the form of the lines did not change, but their 

 character did ; for in place of an equal illumination at all parts, 

 they assumed a granular character ; i. e. parts near to each other 

 were of different degrees of brightness, and the lines seemed to 

 be dotted iti with light. These enduring lines were not the 

 mere effect of impressions on the eye ; for, taught by former 

 observations, I could distinguish them from such a result by 

 directing the axis of the eye from the point directly regarded, to 

 another part of the luminous map, and to another, and back to 

 the first point, namely the angle on the >— , before the lines 

 were quite gone. The form did not move with the eyes, but 

 was fixed on the sky, and remained there, during its short exist- 

 ence, undisturbed in place. As I have already said, I have on 

 diff"erent occasions noticed this phsenomeuon four or five times. 

 . What is the cause of this effect ? The most probable guess 

 seems to me to be, that it is due to a highly exalted phospho- 

 rescent condition of the particles of cloud, along or through which, 

 the electric discharge has passed ; and perhaps an experiment- 

 alist might find means of realizing it in some degree. I believe 

 that like luminous traces have been observed upon sugar and 

 some other bodies when the electric discharge has been made 

 over them. 



M. F. 



