supposed forms of Lightnings 105 



it was simply this line more brilliant at its upper than at its 

 lower part. Some writers have described curved flashes of 

 lightning, the electric fluid having parted from the clouds, 

 gone obliquely downwards to the sea, and then turned up- 

 wards to the clouds again : this effect I have occasionally seen, 

 and have always found it to be merely the illuminated edge of 

 a cloud. 



I have seen cases of this kind in which the flash appeared 

 to divide in its course, one stream separating into two ; and 

 when flashes seen at a distance are supposed to exhibit this 

 rare condition, it is very important the observer should be 

 aware of this very probable cause of deception. 



I have also frequently seen, and others with me, a flash 

 having an apparently sensible duration, as if it were a mo- 

 mentary stream, rather than that sudden, brief flash which the 

 electric spark always presents, whose duration even Wheat- 

 stone could not appreciate. This I attribute to two or three 

 flashes occurring very suddenly in succession at the same 

 place, or nearly so, and illuminating the same edge of a 

 cloud. 



The effect I have described can frequently be easily traced 

 to its cause, and when thus traced best prepares the mind to 

 appreciate the mistakes it may lead, and has led, to in the 

 character, shape and condition of the lightning flash. It often 

 happens at the sea-side, that, after a fine day, clouds will to- 

 wards evening collect over the sea on the horizon, and light- 

 ning will flash about and amongst them, recurring at intervals 

 as short as two or three seconds, for an hour or more together. 

 At such times the observer may think he sees the light- 

 ning of a flash; but if he waits till the next illumination, or 

 some future one, takes place, he will perceive that the flash 

 appears a second time in the same place, and with the same 

 form ; or perhaps it has travelled a little distance to the left or 

 right, and yet has the same form as before. Sometimes an 

 apparent flash, having the same shape, has occurred three or 

 four times in succession ; and sometimes it has happened that 

 a certain shaped flash having appeared in a certain place, 

 other flashes have appeared in other places, then the first has 

 reappeared in its place, and even the others again in their 

 places. Now in all these cases it was simply the illuminated 

 edges of clouds that were seen, and not the real flashes of 

 lightning. These forms frequently appear to be in the cloud, 

 and yet are not distinguishable till the lightning occurs. It is 

 easy, however, to understand why they are then only developed, 

 for that which appears in the distance to be one dull mass of 

 cloud, distinguishable in figure only at its principal outline, 

 often consists of many subordinate and well-shaped masses, 



